CN111313379B

CN111313379B - Disconnection protection method for comparing line voltage on two sides of line and spare power automatic switching

Info

Publication number: CN111313379B
Application number: CN201911247191.0A
Authority: CN
Inventors: 刘昶; 胡浩; 孙东杰; 杨静; 马骏毅; 朱燕妮; 朱文韬; 周杨; 于晓蒙
Original assignee: State Grid Jiangsu Electric Power Co ltd Zhenjiang Power Supply Branch
Current assignee: State Grid Jiangsu Electric Power Co ltd Zhenjiang Power Supply Branch
Priority date: 2019-12-09
Filing date: 2019-12-09
Publication date: 2021-03-30
Anticipated expiration: 2039-12-09
Also published as: CN111313379A

Abstract

The invention discloses a disconnection protection method for comparing line voltages at two sides of a line with the matching of spare power automatic switching. According to the invention, the voltage information of two sides of the line is transmitted through the optical fiber channel of the line, the line voltages of two sides of the line are compared to identify the line breakage, the circuit breaker at the power supply side of the line is tripped or the circuit breaker at the load side is tripped, and then the spare power supply automatic switching action of the transformer station at the load end is used for starting the incoming line breaker to trip and closing the circuit breaker of the spare power supply, so that the transformer losing the power supply is recovered to the spare power supply for supplying power, the influence of the phase-lacking power supply of the transformer on the power grid. The method of the invention is implemented by adopting the line protection devices at two sides of the line, and does not need to increase hardware equipment.

Description

Disconnection protection method for comparing line voltage on two sides of line and spare power automatic switching

Technical Field

The invention relates to a disconnection protection method for comparing line voltage on two sides of a line and matching with a spare power automatic switch, and belongs to the technical field of protection and control of a power transmission and distribution network.

Background

At present, the line disconnection phenomenon of 3-66 kV (including 3, 6, 10, 20, 35 and 66kV) lines occurs in power grids in various places, and the line disconnection causes the phase-loss operation of a transformer supplied by the lines, so that the three-phase voltage of the transformer is asymmetric, the influence is generated on load power supply, electrical equipment can be damaged, for example, a motor is damaged due to the phase-loss operation. In the prior art, no relay protection device and method specially aiming at the disconnection of a 3-66 kV line exist. The invention provides a single-phase disconnection relay protection method which is used for transmitting voltage information of two sides of a line through a line optical fiber channel at a load-end substation, comparing line voltages of two sides of the line, identifying 3-66 kV line disconnection, tripping a line power supply-side circuit breaker or a load-side circuit breaker and recovering power supply through a 3-66 kV backup power automatic switch of the load-end substation.

Disclosure of Invention

The invention aims to provide a disconnection protection method for comparing line voltages on two sides of a line with a spare power automatic switching device, which is used for a load end 3-66 kV transformer substation, transmits voltage information on two sides of the line through a line optical fiber channel, compares the line voltages on two sides of the line to identify line disconnection, and is used for a circuit breaker on a power supply side or a load side of a trip circuit, and is used for a single-phase disconnection relay protection method for recovering power supply through the spare power automatic switching device of the load end 3-66 kV transformer substation.

The purpose of the invention is realized by the following technical scheme:

a disconnection protection method for comparing line voltage on two sides of a line with matching of spare power automatic switching comprises the following steps:

judging the condition of line breaking starting circuit-jumping power supply side circuit breaker or load side circuit breaker and recovering power supply by spare power automatic switch

1.1 judging the No. 1 circuit disconnection tripping No. 1 disconnection circuit power supply side circuit breaker 4DL and the load end backup automatic switching starting combined backup power supply circuit breaker 2DL or 3DL, and starting No. 1 circuit disconnection alarm conditions:

a. acquiring voltage value U of secondary AB line of I-section bus PT of load-end transformer substation_abBC line voltage value U_bcCA line voltage value U_ca；

(1) A load end incoming line breaker 1DL of the No. 1 power line is at a switching-on position;

(2) load end I section bus PT secondary AB line voltage value U_abBC line voltage value U_bcCA line voltage value U_caOf the three line voltage values, two values are satisfied at 0.45E_abTo 0.635E_abBetween, a value of 0.9E_abTo 1.1E_abE is_abThe rated line voltage value of the power supply;

when the conditions are met, the voltage of the first-section bus of the load-end substation is abnormal (hereinafter referred to as voltage abnormity), and the voltage abnormity signal of the first-section bus of the load-end substation are transmitted to disconnection protection in power end line protection of the first-section bus of the upper-stage substation through an optical fiber channel of the No. 1 power line optical fiber differential protection;

b. acquiring secondary AB line voltage value U of bus PT corresponding to upper-level transformer substation_abBC line voltage value U_bcCA line voltage value U_ca；

(1) Power supply end corresponding bus PT secondary AB line voltage value U_abGreater than or equal to 0.9E_ab1.1E or less_ab；

(2) Power supply end corresponding bus PT secondary BC line voltage value U_bcGreater than or equal to 0.9E_ab1.1E or less_ab；

(3) Power supply end corresponding bus PT secondary CA line voltage value U_caGreater than or equal to 0.9E_ab1.1E or less_ab；

(4) The power supply end line breaker 4DL of the line 1 is at the switching-on position;

all the conditions are met, and the condition shows that 3 line voltages of the transformer substation bus on the upper power supply side are symmetrical (the amplitudes are basically equal), namely the voltage on the power supply side is normal (the voltage is normal for short);

when the corresponding bus voltage of the power supply side transformer substation is normal and the received bus voltage of the I section of the load side transformer substation is abnormal, identifying and judging the disconnection of the No. 1 power supply line, performing disconnection protection in the line protection of the superior transformer substation, and jumping a No. 1 power supply line power supply side circuit breaker 4 DL; as the No. 1 power supply circuit loses power supply, the load end transformer substation is in standby automatic switching action, the No. 1 power supply incoming line breaker 1DL is started to be tripped off, and the standby power supply breaker 2DL or 3DL is closed, so that the transformer losing the power supply is recovered to the standby power supply circuit for supplying power; simultaneously starting No. 1 line disconnection alarm;

1.2 judging No. 2 circuit break tripping No. 2 circuit break line power supply side circuit breaker 5DL and starting by load end spare power automatic switching to close spare power supply circuit breaker 1DL or 3DL, and starting No. 2 circuit break alarm condition:

a. acquiring secondary AB line voltage value U of II-section bus PT of load-end transformer substation_abBC line voltage value U_bcCA line voltage value U_ca；

(1) A load end incoming line breaker 2DL of the No. 2 power line is at the switching-on position;

(2) load end II section generating line PT secondary AB line voltage value U_abBC line voltage value U_bcCA line voltage value U_caOf the three line voltage values, two values are satisfied at 0.45E_abTo 0.635E_abBetween, a value of 0.9E_abTo 1.1E_ab；

When the condition is met, the voltage of the second section of the bus of the load-end substation is abnormal, and the voltage abnormal signal of the second section of the bus of the load-end substation are transmitted to the disconnection protection in the power end line protection of the No. 1 line of the upper-level substation through the optical fiber channel of the No. 2 power line optical fiber differential protection;

(4) The power supply end circuit breaker 5DL of the No. 2 circuit is at the switching-on position;

when all the conditions are met, the condition indicates that the corresponding bus voltage of the superior substation is normal;

when the corresponding bus voltage of the upper-level substation is normal and the received bus voltage of the second section of the load-side substation is abnormal, identifying and judging that the No. 2 power line is broken, carrying out broken line protection in the line protection of the upper-level substation, and tripping a power-side circuit breaker 5DL of the No. 2 power line; as the No. 2 power supply circuit loses power supply, the load end transformer substation is in standby automatic switching action, the No. 2 power supply incoming line breaker 2DL is started to be tripped off, and the standby power supply breaker 1DL or 3DL is closed, so that the transformer losing the power supply is recovered to the standby power supply circuit for supplying power; simultaneously starting No. 2 line disconnection alarm;

1.3 judging No. 1 circuit disconnection jumping No. 1 disconnection circuit load side circuit breaker 1DL, starting combined standby power supply circuit breaker 2DL or 3DL by load end backup power automatic switching, and starting No. 1 circuit disconnection alarm condition:

(2) load end I section bus PT secondary AB line voltage value U_abBC line voltage value U_bcCA line voltage value U_caOf the three line voltage values, two values are satisfied at 0.45E_abTo 0.635E_abOne at 0.9E_abTo 1.1E_abTo (c) to (d);

the conditions are all met, and the condition indicates that the voltage of the I-section bus of the load-end transformer substation is abnormal (hereinafter referred to as voltage abnormity);

when all the conditions are met, the voltage of the bus of the transformer substation on the upper power supply side is normal; the normal voltage signal is transmitted to the disconnection protection in the load substation line protection of the No. 1 line through an optical fiber channel of the No. 1 power supply line optical fiber differential protection;

when the corresponding bus voltage of a power side transformer substation is normal and the bus voltage of a first section of a load side transformer substation is abnormal, identifying and judging that a No. 1 power line is broken, carrying out broken line protection in the line protection of the load side transformer substation, tripping a No. 1 power line load side circuit breaker 1DL, starting a switch-on standby power circuit breaker 2DL or 3DL by the load side transformer substation to enable a transformer losing a power supply to recover to the standby power line for power supply; simultaneously starting No. 1 line disconnection alarm;

1.4 judging the load side circuit breaker 2DL of No. 2 circuit disconnection jump No. 2 disconnection circuit and the backup power supply circuit breaker 1DL or 3DL started by the load side backup power automatic switch, and starting the condition of No. 2 circuit disconnection alarm:

(2) load end II section generating line PT secondary AB line voltage value U_abBC line voltage value U_bcCA line voltage value U_caOf the three line voltage values, two values are satisfied at 0.45E_abTo 0.635E_abOne at 0.9E_abTo 1.1E_ab；

When the conditions are met, the voltage abnormality of the second section of the bus of the load-end substation is represented;

when all the conditions are met, the condition indicates that the corresponding bus voltage of the superior substation is normal; the normal voltage signal is transmitted to the disconnection protection in the load substation line protection of the No. 2 line through an optical fiber channel of the No. 2 power supply line optical fiber differential protection;

when the received bus voltage corresponding to the upper-level transformer substation is normal and the bus voltage of the second section of the load-side transformer substation is abnormal, identifying and judging that the No. 2 power supply circuit is disconnected, performing disconnection protection in the protection of the circuit of the upper-level transformer substation, tripping a No. 2 power supply circuit load-side circuit breaker 2DL, and starting the closing of a standby power supply circuit breaker 1DL or 3DL by the spare power automatic switching action of the load-side transformer substation to enable the transformer losing power supply to recover to the standby power supply circuit for power supply; and simultaneously, starting No. 2 line disconnection alarm.

The object of the invention can be further achieved by the following technical measures:

the disconnection protection method for comparing the line voltage on two sides of the line and the spare power automatic switching is applied to a mode that a neutral point of a transformer is not grounded or is grounded through an arc suppression coil and a low-resistance grounding system.

The line break protection method for comparing the line voltage at two sides of the line and the spare power automatic switching is adopted, and the rated line voltage value E of the PT secondary side_abIs 100V.

According to the wire breakage protection method for comparing the line voltage on the two sides of the line and the matching of the spare power automatic switching, t1 is 0.1-0.2 second when three phases are not in phase when the breaker is switched on.

Compared with the prior art, the invention has the beneficial effects that:

1. the method fully utilizes the fault characteristics of the secondary voltage of the power supply end and the load end substation bus PT during the single-phase line break of the line, compares the voltages of the buses at the two ends of the line, and identifies the single-phase line break and line jump circuit breaker at the power supply side or the load side, thereby being simple and easy to implement.

2. The invention adopts a relay protection scheme that the voltage information at two sides of the line is transmitted through the optical fiber channel of the line, the line voltage at two sides of the line is compared to identify the line break, the circuit breaker at the power supply side of the line is tripped or the circuit breaker at the load side is tripped, then the substation spare power automatic switching action at the load end is used for starting the incoming line breaker to trip and closing the circuit breaker at the spare power supply, so that the transformer losing the power supply is recovered to the power supply on the spare power supply, thereby effectively preventing the influence of the phase-lacking power supply of the transformer on the power grid and the power.

3. The method of the invention is implemented by adopting the line protection devices at two sides of the line, and does not need to increase hardware equipment.

Drawings

FIG. 1 is a schematic diagram of a primary system of a superior substation with 35kV side not grounded or grounded through an arc suppression coil;

FIG. 2 is a vector diagram of the voltage of a 35kV bus on the power supply side without grounding or through arc suppression coils;

FIG. 3 is a vector diagram of the voltage of a 35kV bus on the load side without grounding or through an arc suppression coil;

FIG. 4 is a schematic diagram of a primary system with a 35kV line break and a load side line break grounded;

FIG. 5 is a vector diagram of the voltage of a 35kV bus on the load side at a load side disconnection point;

FIG. 6 is a schematic diagram of a primary system with a 35kV line broken and a power supply side grounded;

FIG. 7 is a vector diagram of the voltage of a 35kV bus at the ground power supply side at a power supply side disconnection;

FIG. 8 is a vector diagram of the voltage of a 35kV bus at the grounded load side at the power supply side disconnection;

fig. 9 is a schematic diagram of a primary system of a superior substation with 35kV side grounded through a resistor;

FIG. 10 is a vector diagram of 35kV bus voltage at the 35kV side of the upper-level substation via the resistance grounding power supply side;

fig. 11 is a voltage vector diagram of a 35kV bus at a 35kV side of an upper-level substation through a resistance grounding load side;

FIG. 12 is a schematic diagram of a primary system with a 35kV line break and a load side line break grounded;

FIG. 13 is a vector diagram of the voltage of a 35kV bus at the load side which is grounded at a load side disconnection;

FIG. 14 is a schematic diagram of a 35kV primary system with a power supply side disconnected and a ground connection;

FIG. 15 is a schematic diagram of the 35kV single-phase disconnection protection of the invention comparing the line voltage at two sides of the power supply side and the spare power automatic switching;

FIG. 16 is a schematic diagram of the protection of 35kV single-phase disconnection comparing the line voltage on two sides of the load side and the spare power automatic switching;

FIG. 17 is a sectional primary main wiring diagram of a single bus of a 35kV substation;

FIG. 18 is a primary main wiring diagram of an inner bridge of a 35kV substation;

FIG. 19 is a diagram of a primary main wiring of an enlarged inner bridge of a 35kV substation;

fig. 20 is a primary main connection of a 35kV line transformer set of a 35kV substation.

Detailed Description

The invention is further described with reference to the following figures and specific examples.

Firstly, analyzing fault characteristics by taking 35kV line disconnection as an example (3, 6, 10, 20 and 66kV lines are the same):

1.1 ungrounded or arc-suppression coil grounding system

1.1.135 kV line broken wire

Fig. 1 is a schematic diagram of a 35kV primary disconnection system, taking an a-phase stub as an example. The 35kV side of the upper-level transformer substation is not grounded or is grounded through an arc suppression coil, and the 35kV neutral point of the 35kV transformer substation on the load side is not grounded. The power supply potentials at 35kV sides of the upper-level transformer substation are respectively set as E_A、E_B、E_C，U_NSetting alpha for the 35kV neutral point voltage of the transformer of the power side transformer substationAnd when the line is broken, the capacitance to ground of the bus side of the transformer substation from the broken line to the upper-level transformer substation is alpha C, and the capacitance to ground of the 35kV bus of the transformer substation from the broken line to the load side is (1-alpha) C.

1. Power supply side bus voltage analysis

Analyzing to obtain the voltage of a bus at the 35kV side of the upper-level transformer substation as follows:

(1) in the formula (I), the compound is shown in the specification,

the voltage of a power side 35kV bus A1B1 line, the voltage of a B1C1 line and the voltage of a C1A1 line are respectively.

The voltage of the 35kV side power line of the upper-level transformer substation is equal. The vector diagram of the voltage of the 35kV bus on the power supply side is shown in fig. 2, and as can be seen from fig. 2, when the phase A of the 35kV line is disconnected, the voltage of the three-phase line of the 35kV bus of the upper-level substation is unchanged and keeps symmetry. In the figure, alpha varies between 0 and 1, and 0 point is 0 in FIG. 2_α＝0To 0_α＝1When α is 1, point 0 is 0_α＝1At the point, when α is 0, 0 is 0_α＝0(the same applies below).

2. Load side bus voltage analysis

The 35kV load side bus voltage is analyzed as follows:

(2) in the formula (I), the compound is shown in the specification,

the line voltage of the load side 35kV bus A2B2, the line voltage of B2C2 and the line voltage of C2A2 are shown in a vector diagram of the load side 35kV bus in figure 3.

As can be seen from FIG. 3, when the 35kV line is disconnected, the load side

Is composed of

And

in the opposite direction and of magnitude

1.1.235 kV line disconnection and load side disconnection grounding

Fig. 4 is a schematic diagram of a 35kV line break and load side line break grounding primary system, taking an a-phase stub as an example. The 35kV side of the upper-level transformer substation is not grounded, and the 35kV neutral point of the 35kV transformer substation on the load side is not grounded. The power supply potentials at 35kV sides of the upper-level transformer substation are respectively set as E_A、E_B、E_C，U_NThe voltage of a 35kV neutral point of a transformer substation on a power supply side is alpha C on the bus side of a transformer substation from a broken line to a superior substation, and the capacitance of the 35kV bus of the transformer substation from the broken line to a load side is (1-alpha) C.

1. Power supply side bus voltage analysis

The analysis was as in 1.1.1.

2. Load side bus voltage analysis

The 35kV load side bus voltage is analyzed as follows:

the vector diagram of the 35kV bus voltage on the load side is shown in figure 5.

As can be seen from FIG. 5, when the 35kV line is broken and the load side broken line is grounded,

is equal to

Alpha is in the position of the power supply side bus along with the difference of the distance of the broken line close to the power supply side bus0 to 1 while varying

In that

To a change of 0, point 0 being as in FIG. 5 0_α＝0To 0_α＝1The number of the intermediate change is changed,

is as large as

Change to E_BWhile varying between

Size of (2)

Change to E_CAnd (4) change.

1.1.335 kV line disconnection and power supply side disconnection point grounding

Fig. 6 is a schematic diagram of a primary system with a 35kV line broken and a power supply side grounded, taking an a-phase short line as an example. The 35kV side of the upper-level transformer substation is not grounded, and the 35kV neutral point of the 35kV transformer substation on the load side is not grounded. The power supply potentials at 35kV sides of the upper-level transformer substation are respectively set as E_A、E_B、E_C，U_NThe voltage of a 35kV neutral point of a transformer substation on a power supply side is alpha C on the bus side of a transformer substation from a broken line to a superior substation, and the capacitance of the 35kV bus of the transformer substation from the broken line to a load side is (1-alpha) C.

1. Power supply side bus voltage analysis

Analyzing the voltage of a bus at the 35kV side of the upper-level transformer substation:

the vector diagram of the 35kV bus voltage at the power supply side is shown in figure 7.

As can be seen from fig. 7, when the 35kV line is disconnected and the power supply side is grounded, the three line voltages are constant and symmetrical.

2. Load side bus voltage analysis

The 35kV load side bus voltage is analyzed as follows:

the vector diagram of the 35kV bus voltage on the load side is shown in figure 8.

When the 35kV line is broken, the load side

Is composed of

And

in the opposite direction and of magnitude

1.2 grounding System via a resistor

1.2.135 kV line broken wire

Fig. 9 is a schematic diagram of a 35kV primary disconnection system, taking an a-phase stub as an example. The 35KV power supply system of the 35kV side transformer substation of the upper-level transformer substation is grounded through a resistor (R is generally 10, 20 and 100 omega). The power supply potentials at 35kV sides of the upper-level transformer substation are respectively set as E_A、E_B、E_C，U_NIf alpha is broken for the 35kV neutral point voltage of the transformer of the power side transformer substation, the capacitance to ground of the bus side of the transformer substation from the broken line to the upper level is alpha C, and the capacitance to ground of the 35kV bus of the transformer substation from the broken line to the load side is (1-alpha) C.

1. Power supply side bus voltage analysis

(6) in the formula (I), the compound is shown in the specification,

the voltage of a power side 35kV bus A1B1 line, the voltage of a B1C1 line and the voltage of a C1A1 line are respectively. The vector diagram of the 35kV bus voltage on the power supply side is shown in FIG. 10.

As can be seen from fig. 10, when a phase a of the 35kV line is disconnected, the voltages of the three-phase lines of the 35kV bus of the upper-level substation are unchanged and are kept symmetrical. With the distance of the broken line close to the power supply side bus bar different, the 0 point is 0 in FIG. 10_α＝0To 0_α＝1When α is 1, point 0 is 0_α＝1At the point, when α is 0, 0 is 0_α＝0(same below) with U_NAt about ω CE_AThe variation from R to 0 (the cable line capacitance C is generally less than or equal to 0.55 mu F, and the overhead line is even smaller, so U_NIs a very small value, and is 0.55 mu F, U according to the grounding resistance of 20 omega, C_NIs 3.45^-3E_AAnd so can be ignored).

2. Load side bus voltage analysis

The 35kV load side bus voltage is analyzed as follows:

(7) in the formula (I), the compound is shown in the specification,

the line voltage of the load side 35kV bus A2B2, the line voltage of B2C2 and the line voltage of C2A2 are shown in a vector diagram of the load side 35kV bus in the figure 11.

As can be seen from FIG. 11, when the 35kV line is disconnected, the load side

Is composed of

And

in the opposite direction and of magnitude

1.2.235 kV line disconnection and load side disconnection grounding

Fig. 12 is a schematic diagram of a 35kV line break and load side line break grounding primary system, taking an a-phase stub as an example. The 35KV power supply system of the 35kV side transformer substation of the upper-level transformer substation is grounded through a resistor. The power supply potentials at 35kV sides of the upper-level transformer substation are respectively set as E_A、E_B、E_C，U_NThe voltage of a 35kV neutral point of a transformer substation on a power supply side is alpha C on the bus side of a transformer substation from a broken line to a superior substation, and the capacitance of the 35kV bus of the transformer substation from the broken line to a load side is (1-alpha) C.

1. Power supply side bus voltage analysis

The analysis was as in 1.2.1.

2. Load side bus voltage analysis

The 35kV load side bus voltage is analyzed as follows:

the vector diagram of the 35kV bus voltage on the load side is shown in FIG. 13.

As can be seen from FIG. 13, when the 35kV line is disconnected and the load side disconnection is grounded, U is turned off_B2C2Is equal to E_BCAnd the distance is different along with the distance of the broken line close to the power supply side bus. Due to U_NCan be ignored, so U_A2B2、U_C2A2Is about equal to E_BAnd E_C。

1.2.335 kV line disconnection and power supply side disconnection point grounding

FIG. 14 is a schematic diagram of a primary system with 35kV disconnection and power supply side disconnectionTake the A phase short line as an example. The 35KV power supply system of the 35kV side transformer substation of the upper-level transformer substation is grounded through a resistor. The power supply potentials at 35kV sides of the upper-level transformer substation are respectively set as E_A、E_B、E_C，U_NThe voltage of a 35kV neutral point of a transformer substation on a power supply side is alpha C on the bus side of a transformer substation from a broken line to a superior substation, and the capacitance of the 35kV bus of the transformer substation from the broken line to a load side is (1-alpha) C.

When the line is broken and the system side is grounded, the fault is a single-phase grounding short circuit fault, so that the zero sequence current protection action of the system transformer substation line trips, and reclosure cannot be coincided.

Analyzing the line breaking fault characteristics of the 3-66 kV line:

for three conditions of ungrounded, arc suppression coil grounded and resistance grounded systems, 35kV line breakage and load side line breakage grounded, 35kV line breakage and power supply side line breakage grounded, the power supply side line voltage is constant and symmetrical (for the resistance grounded systems, when the line breakage and system side grounded, single-phase grounding short circuit fault occurs, the zero-sequence current protection of the line trips actions).

Due to the grounding condition of the broken line of the 35kV line and the broken line of the power supply side, U_NCan be ignored, so for the two conditions of 35kV line disconnection, 35kV line disconnection and grounding at the power supply side disconnection, the load side bus line voltage and the load side

Is equal to

And

in the opposite direction and of magnitude

For 35kV line breakageAnd the load side broken line is grounded,

is equal to

Alpha varies between 0 and 1 according to the distance between the broken line and the bus on the power supply side,

is as large as

Change to E_BWhile varying between

Is as large as

Change to E_CAnd (4) change.

Similarly, when a 3-66 kV line is broken, the bus line voltages on two sides of the line have the same fault characteristics.

The technical scheme of the method of the invention is as follows:

the transmission and distribution network applied by the method is 35kV single-bus subsection primary main connection (including 35kV single-bus primary main connection), 35kV inner bridging connection (shown in figure 18), 35kV expansion inner bridging connection (shown in figure 19) and 35kV line transformation group primary main connection (shown in figure 20) of a 35kV substation. Taking the primary main connection of a 35kV single bus subsection in a 35kV substation as an example, the protection method of other primary main connections is similar. The 35kV single-bus subsection primary main wiring general structure of the 35kV substation is as follows: the No. 1 power supply incoming line branch equipment and the No. 2 power supply incoming line branch equipment are respectively connected with a 35kV I section bus and a 35kV II section bus; a segmented circuit breaker 3DL is arranged between the 35kV first-segment bus and the second-segment bus, and the segmented circuit breaker 3DL is connected with a segmented current transformer CT in series; the circuit breaker 1DL is arranged at the interval of the No. 1 power supply inlet branch circuit, the circuit breaker 2DL is arranged at the interval of the No. 2 power supply inlet branch circuit, and the No. 1 power supply inlet branch circuit and the No. 2 power supply inlet branch circuit are respectively connected with a current transformer CT1 and a current transformer CT2 in series; in addition, the 35kV I section bus is also connected with a No. 1 transformer branch and a 35kV voltage transformer PT 1; the 35kV II section bus is also connected with a No. 2 transformer branch and a 35kV voltage transformer PT 2. There is circuit breaker 4DL No. 1 power inlet wire circuit power supply side, and there is circuit breaker 5DL No. 2 power inlet wire circuit power supply side. No. 1 power supply inlet wire power end 35kV generating line connects 35kV PT3, and No. 2 power supply inlet wire power end 35kV generating line connects 35kV PT 4. The 35kV line is provided with an optical fiber channel and line optical fiber differential protection.

Aiming at the 35kV single-bus subsection primary main connection, a scheme that voltage information on two sides of a line is transmitted through a 35kV line optical fiber channel, line voltage on two sides of the line is compared to identify the 35kV line disconnection, a 35kV line power supply side circuit breaker or a load side circuit breaker is tripped, and power supply is recovered through a load end 35kV transformer substation spare power automatic switch is implemented in an upper-stage transformer substation, so that the field operation requirement is met.

As shown in fig. 15 and 16, a 35KV line is taken as an example. The invention relates to a disconnection protection method for comparing line voltage at two sides of a line and matching of spare power automatic switching, which comprises the following steps:

1. conditions for judging 35kV line broken line starting tripping 35kV line power supply side circuit breaker or load side circuit breaker and recovering power supply by 35kV spare power automatic switching

1.1 judging the 1 # 35kV line disconnection tripping 1 # 35kV line disconnection line power supply side circuit breaker 4DL and the load end 35kV spare power automatic switching starting combined spare power supply circuit breaker 2DL or 3DL, and starting the 1 # 35kV line disconnection alarm condition

a. Acquiring voltage value U of secondary AB line of I-section bus PT of 35kV transformer substation at load end_abBC line voltage value U_bcCA line voltage value U_ca。

(1) A load end 35kV incoming line breaker 1DL of a No. 1 35kV power line is at a switching-on position;

(2) load end 35kV I section bus PT secondary AB line voltage value U_abBC line voltage value U_bcCA line voltage value U_caThree line voltages, two at 0.45E_abTo 0.635E_abOne at 0.9E_abTo 1.1E_abIn the meantime.

And when the conditions are met, the voltage of the I-section bus of the 35kV transformer substation at the load end is abnormal (hereinafter referred to as abnormal voltage), and the voltage and the I-section bus voltage abnormal signal of the 35kV transformer substation at the load end are transmitted to 35kV disconnection protection in the 35kV line protection of the power end 35kV line of the upper-level transformer substation 1 through an optical fiber channel of the 35kV power line optical fiber differential protection.

b. Acquiring secondary AB line voltage value U of 35kV bus PT corresponding to upper-level transformer substation_abBC line voltage value U_bcCA line voltage value U_ca。

(1) Power end corresponds 35kV generating line PT secondary AB line voltage value U_abGreater than or equal to 0.9E_ab1.1E or less_ab；

(2) Power end corresponds 35kV generating line PT secondary BC line voltage value U_bcGreater than or equal to 0.9E_ab1.1E or less_ab；

(3) Power end corresponds 35kV generating line PT secondary CA line voltage value U_caGreater than or equal to 0.9E_ab1.1E or less_ab；

(4) The power supply end 35kV line breaker 4DL of the No. 1 35kV line is at the on position.

All the conditions are met, and the condition shows that 3 line voltages of 35kV buses of the transformer substation on the upper power supply side are symmetrical (the amplitudes are basically equal), namely the voltage on the power supply side is normal (the voltage is normal for short).

When the voltage of a 35kV bus corresponding to the power side transformer substation is normal and the voltage of a first section of bus of the load end 35kV transformer substation is abnormal, the No. 1 35kV power line is identified and judged, the 35kV power line is protected in the protection of the 35kV line of the upper-level transformer substation, and the No. 1 35kV power line power side circuit breaker 4DL is jumped. As the No. 1 35kV power line loses power, the load end 35kV transformer substation 35kV spare power automatic switching acts, the No. 1 35kV power incoming line breaker 1DL is started to be tripped off, and the spare power supply breaker 2DL or 3DL is closed, so that the transformer losing the power supply is recovered to the spare power line for power supply. And simultaneously, starting No. 1 35kV line disconnection alarm.

1.2 judging the condition of No. 2 35kV line disconnection tripping No. 2 kV line disconnection line power supply side circuit breaker 5DL and the condition of No. 2 kV line disconnection alarm starting No. 35kV line disconnection alarm by starting the standby power supply circuit breaker 1DL or 3DL by the load end 35kV backup power automatic switching device

a. Acquiring secondary AB line voltage value U of II-section bus PT of load-end 35kV transformer substation_abBC line voltage value U_bcCA line voltage value U_ca。

(1) A load end 35kV incoming line breaker 2DL of a No. 2 35kV power line is at a switching-on position;

(2) load end 35kV II section generating line PT secondary AB line voltage value U_abBC line voltage value U_bcCA line voltage value U_caThree line voltages, two at 0.45E_abTo 0.635E_abOne at 0.9E_abTo 1.1E_ab；

And when the conditions are met, indicating that the voltage of the II-section bus of the 35kV transformer substation at the load end is abnormal, and transmitting the voltage and the abnormal signal of the voltage of the II-section bus of the 35kV transformer substation at the load end to 35kV disconnection protection in the protection of the 35kV circuit at the power end of the 1 # 35kV circuit of the upper-level transformer substation through an optical fiber channel of 2 # 35kV power circuit.

(4) And a power supply end 35kV line breaker 5DL of the No. 2 35kV line is at the switching-on position.

And the conditions are all met, and the condition indicates that the 35kV bus voltage corresponding to the upper-level transformer substation is normal.

When the voltage of the 35kV bus corresponding to the upper-level substation is normal and the voltage of the II-section bus of the 35kV substation at the load end is abnormal, identifying and judging that the No. 2 35kV power line is broken, performing 35kV broken line protection in the 35kV line protection of the upper-level substation, and tripping a No. 2 35kV power line power-side circuit breaker 5 DL. Because the No. 2 35kV power line loses power, the load end 35kV transformer substation 35kV spare power automatic switching acts, the No. 2 kV power incoming line breaker 2DL is started to be tripped off, and the spare power supply breaker 1DL or 3DL is closed, so that the transformer losing the power supply is recovered to the spare power line for power supply. And simultaneously, starting No. 2 35kV line disconnection alarm.

1.3 judging No. 1 35kV line disconnection tripping No. 1 No. 35kV line disconnection line load side circuit breaker 1DL, starting combined standby power supply circuit breaker 2DL or 3DL by load end 35kV backup power automatic switching, and starting No. 1 No. 35kV line disconnection alarm condition

The conditions are met, and the voltage abnormity (hereinafter referred to as voltage abnormity) of the I-section bus line of the 35kV transformer substation at the load end is shown.

And when all the conditions are met, the voltage of the 35kV bus of the upper-level power supply side transformer substation is normal. And transmitting the normal voltage signal to 35kV disconnection protection in 35kV line protection of a 35kV transformer substation loaded with the No. 1 35kV line through an optical fiber channel of the No. 1 35kV power line optical fiber differential protection.

When the received voltage of a 35kV bus corresponding to a power side transformer substation is normal and the voltage of a first section of the bus of a load end 35kV transformer substation is abnormal, identifying and judging that a No. 1 35kV power line is broken, performing 35kV broken line protection in the 35kV line protection of the load end 35kV transformer substation, jumping a No. 1 35kV power line load side circuit breaker 1DL, performing 35kV spare power automatic switching action of the load end 35kV transformer substation, starting up a closed spare power circuit breaker 2DL or 3DL, and enabling a transformer losing power to recover to the spare power line for power supply. And simultaneously, starting No. 1 35kV line disconnection alarm.

1.4 judging the condition of 2 # 35kV line disconnection tripping 2 # 35kV line disconnection line load side circuit breaker 2DL and starting combined standby power supply circuit breaker 1DL or 3DL by load end 35kV backup power automatic switching, and starting 2 # 35kV line disconnection alarm

And when the conditions are met, the abnormal voltage of the II-section bus of the 35kV transformer substation at the load end is represented.

(1) Power source terminal correspondence 35kV bus PT secondary AB line voltage value U_abGreater than or equal to 0.9E_ab1.1E or less_ab；

And the conditions are all met, and the condition indicates that the 35kV bus voltage corresponding to the upper-level transformer substation is normal. And transmitting the normal voltage signal to 35kV disconnection protection in 35kV line protection of a 35kV transformer substation loaded with 35kV lines of No. 2 35kV power lines through an optical fiber channel of No. 2 35kV power line optical fiber differential protection.

When the received 35kV bus voltage corresponding to the upper-level transformer substation is normal and the II-section bus voltage of the load-end 35kV transformer substation is abnormal, identifying and judging that the No. 2 35kV power line is broken, performing 35kV broken line protection in the 35kV line protection of the upper-level transformer substation, jumping a No. 2 No. 35kV power line load-side circuit breaker 2DL, and starting the closing of the standby power circuit breaker 1DL or 3DL through the 35kV spare power automatic switching action of the load-end 35kV transformer substation to enable the transformer losing the power supply to recover to the standby power line for power supply. And simultaneously, starting No. 2 35kV line disconnection alarm.

1.5 of the above 1.1 to 1.4:

(1) the method can be applied to a transformer neutral point ungrounded mode or arc suppression coil grounding mode and a small-resistance grounding system.

(2) The reason that the circuit breakers 1DL or 2DL and 4DL or 5DL on the two sides of the 35kV power inlet wire are arranged at the switching-on position is as follows: when a 35kV substation with a load end is arranged on a power supply incoming line, the bus voltage far away from the power supply incoming line can also sense the line disconnection information, and the standby power supply circuit breaker for closing of the standby automatic switching can be interfered; in addition, when a line PT is adopted, the power supply incoming line may have other load end 35kV substations, and if the power supply incoming line breaker of the load end 35kV substation trips slowly or refuses tripping, the power supply incoming line breaker of the backup automatic switching device may be interfered, and the backup automatic switching device may not act. The logic can be further optimized by adopting the condition of the 35kV power incoming line breaker at the switching-on position.

(3)E_abFor the rated line voltage value of the power supply, the voltage fluctuation of the power grid is considered, and the voltage fluctuation is considered according to +/-10% of the rated voltage value of the actual power grid, wherein: when the voltage value is larger than or equal to the rated line voltage value, the rated line voltage value of the power grid is considered to be 0.9 times; the rated line voltage value is less than or equal to 1.1 times of the rated voltage value of the power grid.

1.6 after the 35kV line is identified to be broken, the tripping scheme is as follows: (1) tripping off a breaker at the power supply side of the broken line; (2) tripping off a circuit breaker on the load side of the broken line; (3) the circuit breakers on both sides of the line break are tripped together.

And 1.7, for the load side substation bus load which is in open-phase operation due to wire break, automatically transferring the load to the standby line by switching on a standby power supply breaker or a power supply side breaker of the power supply automatic switching tripping open circuit. If the 35kV transformer substation adopts primary main wiring of a 35kV line transformer group, the power supply is recovered by the spare power automatic switching device at the low-voltage side of the transformer substation at the load side.

2. The operation mode of a 35kV neutral point of a main transformer on a first section or a second section of a bus of a load end 35kV transformer substation is ungrounded; 35kV side equipment 35kV spare power automatic switching device. No. 1 and No. 2 power supply 35kV lines are required to be provided with optical fiber channels and line optical fiber differential protection.

3. The method can be implemented in a 35kV line disconnection protection device independent of a power supply end or a load end 35kV transformer substation or in a 35kV line protection device. The method is implemented in a 35kV line protection device, and has the advantage that no hardware equipment is required to be added.

4. The second setting value of the broken line phase PT of the I section bus or the II section bus of the 35kV transformer substation at the load end is as follows:

load end 35kV generating line PT secondary AB line voltage value U_abBC line voltage value U_bcCA line voltage value U_caSetting values of three line voltages are as follows: two of which are greater than or equal to 45% (0.9 x 0.5) and less than or equal to the rated line voltage value

The PT secondary rated line voltage value is 100V, namely more than or equal to 45V and less than or equal to 63.5V; one is more than or equal to 90 percent of the rated line voltage value and less than or equal to 110 percent of the rated line voltage value, namely more than or equal to 90V and less than or equal to 110V.

The PT secondary setting value of the 35kV bus of the power supply end 35kV transformer substation when the 5.35 kV line is broken is as follows:

power end 35kV generating line PT secondary AB line voltage value U_abBC line voltage value U_bcCA line voltage value U_caSetting values of three line voltages are as follows: the PT secondary rated line voltage value is 100V, and is more than or equal to 90 percent of the rated line voltage value and less than or equal to 110 percent of the rated line voltage value, namely more than or equal to 90V and less than or equal to 110V.

6. The method of the invention is characterized in that the setting value of time in the single-phase disconnection relay protection method for recovering power supply by the spare power automatic switching of the load-end 35kV transformer substation is as follows:

t 1: avoiding the three-phase different-period time when the switch is switched on, and taking 0.1-0.2 second;

7. the scheme of the invention can meet the following primary main wiring: (1) a 35kV single-bus subsection primary main wiring of a 35kV transformer substation; (2) a 35kV transformer substation 35kV inner bridge primary main wiring; (3) a 35kV transformer substation 35kV enlarges primary main wiring; (4) a 35kV transformer substation 35kV line group-changing primary main wiring; (5) other primary main connections.

8. For a 35kV line with branch lines, 35kV line breakage protection of pairwise correspondence between a power end-load end substation and each load end substation needs to be implemented.

9. The scheme of the invention for comparing the bus line voltages on two sides of the line can also be used in the case of the disconnection of the 110kV line powered by a single power supply.

An embodiment of the method of the invention is given below (taking fig. 17 and the trip power source side circuit breaker as an example):

mode of operation 1

Under this operational mode, 2DL of No. 2 power circuit breaker, the operation of segmentation circuit breaker 3DL, 1DL of No. 1 power circuit breaker is hot standby, 1DL of No. 1 power circuit breaker branch floodgate position promptly.

For example, if phase A is broken, phase B or phase C is broken similarly. When the phase-A single-phase disconnection fault of the No. 2 35kV power line occurs, the line voltage of the second section of the bus of the load-side transformer substation is sensed to be abnormally operated, but the secondary line voltage of the 35kV bus PT of the power end transformer substation is normal, the single-phase disconnection condition of the No. 2 35kV power line is met, after the time delay t1, the 35kV line disconnection protection in the power end line protection is carried out, and the 5DL of the power-side circuit breaker of the No. 2 35kV power line is jumped. Because No. 2 35kV power supply line loses power, 35kV spare power automatic switching action of a load end 35kV transformer substation trips No. 2DL of a 35kV power supply circuit breaker, 35kV starts a No. 1DL of a 35kV spare power supply circuit breaker to switch on, and a transformer losing the power supply is recovered to a No. 1 spare 35kV power supply line to supply power. And meanwhile, a No. 2 35kV power line single-phase disconnection signal is sent.

Mode of operation 2

Under this operational mode, 1DL of power breaker, 3DL operation of section circuit breaker, 2 # power breaker 2DL are hot standby, 2 # power breaker 2DL separating brake position promptly.

For example, if phase A is broken, phase B or phase C is broken similarly. When the phase-A single-phase disconnection fault of the No. 1 35kV power line occurs, the voltage sense of the I section bus of the load-side transformer substation is abnormally operated, but the secondary line voltage of the PT of the 35kV bus of the power end transformer substation is normal, the single-phase disconnection condition of the No. 1 35kV power line is met, after the time delay t1, the 35kV line disconnection protection in the power end line protection is carried out, and the 4DL of the power-side circuit breaker of the No. 1 35kV power line is jumped. Because No. 1 35kV power line loses the power, the load end 35kV transformer substation 35kV spare power automatic switching action trips No. 1 kV 35kV power circuit breaker 1DL, starts No. 2 kV 35kV spare power circuit breaker 2DL to switch on, makes the transformer that loses the power restore to reserve No. 2 kV power line and supplies power on the way. And simultaneously sending a No. 1 35kV power line single-phase disconnection signal.

Mode for operation 3

Under this operational mode, 1DL of No. 1 power circuit breaker, 2DL of No. 2 power circuit breaker operate, and the hot reserve of section circuit breaker 3DL, section circuit breaker 3DL separating brake position promptly.

No. 1 35kV power line single-phase line break fault

For example, if phase A is broken, phase B or phase C is broken similarly. When the phase-A single-phase disconnection fault of the No. 1 35kV power line occurs, the voltage sense of the I section bus of the load-side transformer substation is abnormally operated, but the secondary line voltage of the PT of the 35kV bus of the power end transformer substation is normal, the single-phase disconnection condition of the No. 1 35kV power line is met, after the time delay t1, the 35kV line disconnection protection in the power end line protection is carried out, and the 4DL of the power-side circuit breaker of the No. 1 35kV power line is jumped. Because No. 1 35kV power supply line loses the power, the load end 35kV transformer substation 35kV spare power automatic switching action trips No. 1 kV 35kV power incoming line breaker 1DL, starts the 35kV spare power supply breaker 3DL to close, and the transformer that loses the power is recovered to the spare No. 2 kV power supply line and is supplied power. And simultaneously sending a No. 1 35kV power line single-phase disconnection signal.

No. 2 35kV power line single-phase line break fault

For example, if phase A is broken, phase B or phase C is broken similarly. When the phase-A single-phase disconnection fault of the No. 2 35kV power line occurs, the voltage sense of the second section of the bus of the load-side transformer substation is abnormally operated, but the secondary line voltage of the 35kV bus PT of the power end transformer substation is normal, the single-phase disconnection condition of the No. 2 35kV power line is met, after the delay t1, the 35kV line disconnection protection in the power end line protection is carried out, and the 5DL of the power-side circuit breaker of the No. 2 35kV power line is jumped. Because No. 2 35kV power supply line loses power, 35kV spare power automatic switching of a load end 35kV transformer substation acts, 2DL of a No. 2 kV power supply incoming line breaker is tripped, 3DL of a 35kV spare power supply breaker is started to be switched on, and a transformer losing the power supply is recovered to a spare No. 1 kV power supply line to supply power. And meanwhile, a No. 2 35kV power line single-phase disconnection signal is sent.

In addition to the above embodiments, the present invention may have other embodiments, and any technical solutions formed by equivalent substitutions or equivalent transformations fall within the scope of the claims of the present invention.

Claims

1. A disconnection protection method for comparing line voltage on two sides of a line with the cooperation of spare power automatic switching is characterized by comprising the following steps:

judging the conditions of starting a circuit breaker at a line-jumping power supply side or a circuit breaker at a load side by line disconnection and recovering power supply by a backup power automatic switch:

1.1 judging the No. 1 line disconnection tripping No. 1 line power supply side circuit breaker 4DL and the load side backup power automatic switching starting combined backup power supply circuit breaker 2DL or 3DL, and starting the No. 1 line disconnection alarming condition:

(1) The 1 st line load side breaker 1DL is in the on position;

(2) load end I section bus PT secondary AB line voltage value U_abBC line voltage value U_bcCA line voltage value U_caOf the three line voltage values, two values are satisfied at 0.45E_abTo 0.635E_abBetween, a value of 0.9E_abTo 1.1E_abE is_abThe voltage value of a secondary side rated line of a power supply PT;

when the conditions are met, the voltage of the first-section bus of the load-end substation is abnormal, and the voltage and the abnormal voltage signal of the first-section bus of the load-end substation are transmitted to the disconnection protection in the power end line protection of the first-stage substation 1 through the optical fiber channel of the No. 1 power line optical fiber differential protection;

(4) The 1 st line power supply side breaker 4DL is in the on position;

all the conditions are met, and 3 line voltages of the buses of the transformer substation on the upper power supply side are symmetrical, namely the voltage on the power supply side is normal;

when the corresponding bus voltage of the power side transformer substation is normal and the received bus voltage of the I section of the load side transformer substation is abnormal, identifying and judging the disconnection of the No. 1 power line, and jumping a No. 1 line power side circuit breaker 4DL through the disconnection protection action in the line protection of the superior transformer substation after the delay time t 1; as the No. 1 power supply circuit loses power supply, the load side transformer substation is in standby automatic switching action, the No. 1 circuit load side circuit breaker 1DL is started to be tripped off, and the standby power supply circuit breaker 2DL or 3DL is closed, so that the transformer losing the power supply is recovered to the standby power supply circuit for supplying power; simultaneously starting No. 1 line disconnection alarm;

1.2 judging No. 2 circuit disconnection tripping No. 2 circuit power supply side circuit breaker 5DL and starting by load end spare power automatic switching to close spare power supply circuit breaker 1DL or 3DL, and starting No. 2 circuit disconnection alarming condition:

(1) The circuit breaker 2DL on the load side of the line 2 is at the closing position;

(4) The circuit breaker 5DL on the line power supply side No. 2 is in the on position;

when the corresponding bus voltage of the upper-level substation is normal and the received bus voltage of the second section of the load-side substation is abnormal, identifying and judging that the No. 2 power supply line is broken, and jumping a No. 2 line power supply side circuit breaker 5DL after the time delay t1 by the broken line protection action in the line protection of the upper-level substation; as the No. 2 power supply circuit loses power supply, the load side transformer substation is in standby automatic switching action, the No. 2 circuit load side circuit breaker 2DL is started to be tripped off, and the standby power supply circuit breaker 1DL or 3DL is closed, so that the transformer losing the power supply is recovered to the standby power supply circuit for supplying power; simultaneously starting No. 2 line disconnection alarm;

1.3 judging No. 1 line disconnection tripping No. 1 line load side circuit breaker 1DL, starting combined standby power supply circuit breaker 2DL or 3DL by load side standby power automatic switching, and starting No. 1 line disconnection alarm condition:

(1) The 1 st line load side breaker 1DL is in the on position;

the conditions are all met, and the voltage of the first-section bus of the load-end substation is abnormal;

(4) The 1 st line power supply side breaker 4DL is in the on position;

when the corresponding bus voltage of the power side transformer substation is normal and the I-section bus voltage of the load side transformer substation is abnormal, identifying and judging that the No. 1 power line is broken, after the delay time t1, performing the broken line protection action in the line protection of the load side transformer substation, jumping the No. 1 line load side circuit breaker 1DL, and starting the on standby power supply circuit breaker 2DL or 3DL by the standby power supply automatic switching action of the load side transformer substation to enable the transformer losing the power supply to recover to the standby power line for power supply; simultaneously starting No. 1 line disconnection alarm;

1.4 judging No. 2 line disconnection tripping No. 2 line load side circuit breaker 2DL and starting by load side backup power automatic switching to close backup power supply circuit breaker 1DL or 3DL, and starting No. 2 line disconnection alarming condition:

when the received corresponding bus voltage of the upper-level transformer substation is normal and the voltage of the second-stage bus of the load-side transformer substation is abnormal, identifying and judging that the No. 2 power supply circuit is broken, after the delay time t1, performing the broken-line protection action in the protection of the circuit of the upper-level transformer substation, jumping the No. 2 circuit load-side circuit breaker 2DL, and starting the closing of the standby power supply circuit breaker 1DL or 3DL by the spare power automatic switching action of the load-side transformer substation to enable the transformer losing the power supply to recover to the standby power supply circuit for power supply; and simultaneously, starting No. 2 line disconnection alarm.

2. The method for protecting the disconnection of the line voltage on two sides of the line in cooperation with the automatic backup power switch as claimed in claim 1, wherein the method is applied to a mode that a neutral point of the transformer is not grounded or is grounded through an arc suppression coil or is grounded through a small resistor.

3. The method for protecting against disconnection of a line by comparing the line voltage across the line with the automatic power switching device of claim 1, wherein the secondary side of the power supply PT is rated for the line voltage E_abIs 100V.

4. The method for protecting the line break by comparing the line voltage on the two sides of the line with the automatic standby switch as claimed in claim 1, wherein the delay time t1 is 0.1-0.2 second when the three phases are not in phase when the breaker is switched on.