STS365T Transformer Protection,

Measurement& Control Device

1、OverView

STS365T transformer protection, measurement, and control device is applicable

to 66KV and lower voltage level station transformer or ground transformer in
non-directly grounded system or small resistance grounded system. This device
can be installed in a panel or locally.
1.1 Configuration of protection functions
a) 2 zones of composite voltage blocking overcurrent protection
b) HV side ZS overcurrent protection
c) LV side ZS overcurrent protection
d) Overload protection (alarm/tripping optional)
e) ZS overvoltage protection (alarm/tripping optional)
f) Undervoltage protection
g) Manual closing acceleration protection
h) 4 lines of non-electric quantity protection
1.2 Measurement and control
1) Measured quantities (current, voltage, power, and power factor etc.)
2) Remote signal acquisition
3) Circuit breaker position, manual tripping, and event remote signaling
4) Normal circuit breaker remote controlled tripping and closing
6) GPS time calibration input

2、Technical parameters

2.1 Rated parameters

2.1.1 Rated DC voltage： 220V/110V

2.1.2 Rated AC data：

 a) Voltage 100 / 3 V

b) Line extraction voltage 100 V OR 100 / 3 V

c) Current 5A OR 1A

d) Frequency 50Hz

2.1.3 Power consumption：

a) DC Normal work：<15W

Action： <25W

b) AC voltage Each phase<0.5VA

c) AC current 5A：Each phase <1VA

1A：Each phase <0.5VA

2.2 Main Technical Performance

2.2.1 Accurate working range of protection elements

Voltage：0.4 V～120V

Current：0.08In－20In

2.2.2 Error of protection element settings

Current element: ≤±5%

Voltage element: ≤±5%

Time element: 0s-1s:<40ms；

>1S: <±2.5％；

3、Protection functions and principle

3.1 Phase-to-phase overcurrent protection

For judgment of 3 zones of overcurrent, judgment logic for each stage is consistent. Operation
conditions are as follows:
1) Iϕ > I dn ; I dn is current setting of stage n and I ϕ is phase current;
2) T > T dn ; T dn is delay setting of stage n.

3.2 Phase-to-phase current inverse time element

Inverse time protection element is a protection element in which operation time naturally matches
amplitude of current in protected line. Through translation of operation curve, whole line
matching can be very easily realized. The device provides 3 common types of inverse time
characteristics: normal inverse time, abnormal inverse time, and extreme inverse time. Inverse
time characteristic is set by “inverse time index” in setting. Formulae of each inverse time
characteristic are as follows:
1) Normal inverse time
0.14tp
t
I
( )0.02  1
Ip

2) Abnormal inverse time

13.5tp
t
I
( ) 1
Ip

3) Extreme inverse time

80tp
t
I 2
( ) 1
Ip

Where: t p is time coefficient in the range (0.05～1); Ip is reference current, I is fault current, and t
is tripping time.
Setting part inverse time time is the product of numerators of above formulae. This time is in
second and its setting range is (0.005～127).
Long time inverse time can also be realized. Expression of long time inverse time is:
Constant time or inverse time mode can be selected for device Phase-to-phase current protection
by setting relevant bits of control word. If inverse time mode is selected, constant time overcurrent
protection stage III will automatically exit operation and functional linking piece of Phase-to-
phase current stage III will become Phase-to-phase current inverse time function enable/disable
linking piece.

3.4 ZS Overcurrent Protection

In case ZS current is used for tripping In default, the device will adopt externally connected ZS
current. In case the following conditions are satisfied, ZS overcurrent protection will act to trip:
1) 3I 0 >I 0n , I 0n is setting of grounding stage n
2) T>T 0n , T 0n is delay setting of grounding stage n
3) Corresponding direction condition is satisfied (if required).

3.5 Closing acceleration

Closing acceleration includes manual closing acceleration and protection acceleration. The
acceleration function can be enabled and disabled via soft linking piece. Starting conditions for
manual closing acceleration circuit:
1) Circuit breaker at tripped position for longer than 30s;
2) Circuit breaker changes from tripped to closed, and acceleration function is open for 3s.
To realize manual closing acceleration function, acceleration linking piece needs to be enabled,
acceleration current and time settings need to be set, and acceleration mode needs to be selected as
post-acceleration mode by control word. If manual closing acceleration protection function is
enabled alone, this can be used for charging protection of sectionalizer or bus coupler circuit
breaker.
Protection acceleration includes pre-acceleration mode and post-reclosing acceleration mode,
which can be selected by control word. This protection is provided with independent current
settings for overcurrent and ZS current acceleration zones and corresponding time settings.
Compared with traditional protections, this protection has more flexible configuration. Also,
undervoltage blocking and negative sequence voltage blocking can be selected for overcurrent
acceleration stage of this protection, but directional blocking is not considered for any acceleration
stage.

3.6 3-Phase Reclosing

3-phase one-shot reclosing and 3-phase two-shot reclosing functions are provided. These

functions are enabled and disabled by corresponding soft linking piece.

3.6.1 Charging conditions

Circuit breaker at close status, no STJ, and there is no reclosing blocking signal. After

15s,charging of reclosing will be completed. During charging, reclosing soft linking piece

indicator will flash. At end of charging, this indicator will glow (no longer flash).

3.6.2 Starting mode

After being charged, reclosing can be started by protection or discrepancy.Start of reclosing

by protection is operation of the protection, that is to say, after judgment of circuit breaker position
and absence of current, reclosing will be open for 10s. In discrepancy reclosing starting mode,

only TWJ contact is used to monitor circuit breaker position.

3.6.3 Reclosing mode

By means of setting “synchronism mode selection”, reclosing mode can be selected: no-

check mode, voltage loss check mode, synchronism check mode, and voltage loss check converted

to synchronism check mode.

3.6.4 Blocking conditions

In case any of the following conditions is satisfied, reclosing will be blocked:

1) After disconnection of control circuit, blocking will occur after a delay of 10s;

2) “Spring unpressed” terminal at high potential, blocking will occur after a delay of 2s;

3) “Block reclosing” terminal at high potential, blocking will occur at once;

4) Circuit breaker at post-tripping position; reclosing will discharge;

5) Circuit breaker at tripped position for 30s; reclosing will discharge.

3.7 Overload protection

The overload protection monitors 3-phase phase currents. Operation conditions are:

1) MAX(I Φ )＞I fh

2) Time delay expired

Where I fh is overload current setting. Overload alarm or tripping is determined by control

word.

3.8 Undervoltage protection

In case system voltage is lower than set voltage, load switch-off will be determined.

Undervoltage element criteria:

1) All 3 inter-phase voltages are lower than undervoltage setting;

2) All currents of 3 phases are less than a setting;

3) Circuit breaker closed;

4) Time delay expired.

3.9 Acceleration function

This device is provided with manual closing post-acceleration function switched on and off

by software linking piece. Startup conditions are:

1) Circuit breaker at tripped position for longer than 30s;

2) Circuit breaker changes from tripped to closed and permitted time spread of acceleration is

3s.

The device is provided with independent current acceleration zone current setting and

corresponding time setting.

3.10 Non-electric quantity protection

This device provides 4 lines of non-electric quantity protection DI, which can be selected as

tripping or alarm by software linking piece. When the software linking piece is switched on, non-

electric quantity protection operates to trip; when it is switched off, this protection only sends

signal.

To allow flexibility, indicators on device panel only show 4 signals: non-electric quantities 1,

2, 3, and 4. Particular significance of each non-electric quantity will be determined according to

particular terminal connections of each project. Normally, in default, non-electric quantity 1 is

heavy gas input end, non-electric quantity 2 is light gas input end, non-electric quantity 3 is

pressure release input end, and non-electric quantity 4 is high oil temperature input end.

3.11 PT disconnection

PT disconnection criteria are as follows:

1) All phase voltages are less than 8V, and some phase (a or c) current exceeds 0.05I N : 3- phase
voltage loss is determined;
2) Sum of triple phase voltages exceeds 8V and minimum line voltage is less than 16V;
3) Sum of triple phase voltages exceeds 8V and difference between maximum line voltage and
minimum line voltage exceeds 16V: 2-phase or single phase VT disconnection is determined.
4 Device setting

4.1 Protection settings list

S/N Name Rage Unit Remark

1 Refer to definition of Control
Code1 0000～FFFF N/A
word 1 (KG1)
2 Refer to definition of Control
Code2 0000～FFFF N/A
word 2 (KG2)
3 I1 0.2～100.0 A
4 I2 0.2～100.0 A
5 T1 0.0～5.00 S
6 T2 0.1～20.00 S
7 IOverload 0.2～100.0 A
8 TAlarmOverload 0.0～9000 S
9 TTripOverload 0.0～9000 S
10 IZScurrent-H 0.1～20.0 A
11 TZScurrent-H 0.0～32.0 S
12 IZScurrent-L 0.1～20.00 A
13 TZScurrent-L 0.1～32.00 S
14 In-L 0.1～20.00 A
15 I-ZS-ITLCP 0.1～100.0 A
16 IAccel 0.2～100.0 A
17 TAccel 0.0～5.000 S
18 ULow-Voltage 0.0～100.0 V
19 TLow-Voltage 0.0～100.0 S
20 IBlock LV 0.2～100.0 A
21 CT Ratio 0.001～10.00
22 PT Ratio 0.01～10.00
Definition of setting control word 1 (KG1):

Place Meaning when set to 1 Meaning when set to 0

15 Check PTLB Don't Check PTLB
14 CT Nominal 1A CT Nominal 5A
13 LZSCT Nominal 5A LZSCT Nominal 1A
3－12 Reserved Reserved
2 No SGACC Reclose Reclose SGACC
1 LZSDT LZSIT
0 Overload Trip Overload Alarm

4.2 List of software linking pieces and description

Name Corresponding function

Overcurrent I1 Overcurrent protection stage I function On/Off

Overcurrent I2 Overcurrent protection stage II function On/Off

Thermal Overload Overload protection function On/Off

Relay Accelerate Manual closing acceleration function On/Off

Residual I0 ZS current function On/Off

Low-Voltage Low_voltage function On/Off

Non-Electricity1 Switching of non-electric quantity 1 function

Non-Electricity2 Switching of non-electric quantity 2 function

Non-Electricity3 Switching of non-electric quantity 3 function

Non-Electricity4 Switching of non-electric quantity 4 function