MCCB Fundamentals
MCCB Fundamentals
MCCB Fundamentals
current limiting
moulded case circuit breaker
LK-Electric Company
The History of LKE Electric
The acronym LKE stands for Lauritz Knudsen Electric. In the late 1970s, the LK
Electric Company was established in Singapore by its parent company, LKE
(Europe) of Denmark. It is to manufacture LK’s range of products, namely, the
Domino, the Tabular of low tension switchboards, the ELC-24 medium voltage
panel and the Ring Main Unit (RMU).
By the mid-80s, with an influx of technology from Denmark, a Components
Division was set up. This was also to cater to the growing demands in the low
voltage sector. Popular products such as the Switch Fuse of the QSA series,
Miniature Circuit Breakers (MCB), Moulded Case Circuit Breakers (MCCB),
Load Break Switches (LK’s ELC-24) and Vacuum Circuit Breakers (LK’s VB-1)
were all produced in the Singapore factory.
In 1992, the LKE Electric Company was established in Malaysia and by
1994, has offices in Zhuhai, Shanghai and Beijing in China. At the same time,
LKE Electric entered into a partnership with the Cubic Modular System A/S
company of Denmark to produce the Cubic Modular Switchboard. And since
then, there is no looking back for the company.
The company is always striving to benefit its customers. Efforts in R&D are
constantly focused, especially with the current era of modern technology, to
enable its products to be of a higher quality and safer, yet at the same time,
aesthetically pleasing and affordable. The company also prides itself with
upgrading of its production facilities, in keeping up with technology, to fulfill
stringent process and quality control requirements. Building a relationship with
the customers and understanding their needs with a zero-defect and
unbeatable range of products are the main objectives of LKE Electric.
Focusing on these objectives, LKE Electric has become an industry leader
with its MCCB Superior Series, 6 & 10kA MCB series, 12kV Load Break Switch
(LBS) and Vacuum Load Break Switch (VLBS) and SF6 Breakers.
1
Superior Series Current Limiting MCCB
LKE Electric’s Superior Series Current Limiting MCCB was developed with the
latest technology for heavy duty usage: a magnetic trip unit for reliable quality
tripping when short circuit occurs, repulse force for moving and fix contact
construction, zero arc distance for the arc chute moulded in with thread nut for the
case and cover and a long lasting BMC material for mounting, super mechanical
and electrical strength.
Application
The current limiting MCCB Superior series is suitable for circuit protection in
individual enclosures, switchboards, lighting and power panels as well as motor-
control centers. The MCCB is designed to protect systems against overload and
short circuits up to 65kA with the full range of accessories.
Mechanism
The MCCB Superior series is designed to be trip-free. This applies when the
breaker contacts open under overload and short circuit conditions and even if the
breaker handle is held at the ON position. To eliminate single phasing, should an
overload or short circuit occur on any one phase, a common trip mechanism will
disconnect all phase contacts of a multipole breaker.
Material
The Superior series circuit breakers’ housing is made of BMC material, which
is unbreakable and has a very high dielectric strength, to ensure the highest level
of insulation. The same material is also used to segregate the live parts in between
the phases.
Accessories
To enhance the Superior series MCCB, internal and external modules can be
fitted onto the breaker. They are as follows:
• shunt trip coil • undervoltage release
• auxiliary switch • alarm switch
• motorized switch • rotary handle
• plug-in kit (draw-out unit) • auxiliary & alarm switch
International Standards
The MCCB Superior series conform and meet the requirements of these
international governing bodies:
• IEC 60947-2 from the International Electrotechnical Committee
• BS EN60947-2 from British Standards
• BT/T14048-2 from China
• NEMA AB-1 from American Standards
• VDE 0660 from Germany.
NEMA
2
Accreditation
of the Superior
Series MCCB
Having undergone rigid testings and achieving
accreditation from SIRIM QAS of Malaysia and
TILVA from China, these test reports affirm the
superior quality of LKE Electric Company’s
Current Limiting Superior Series MCCB.
3
Exceptional Current Limiting
Quick-Breaking Performance
The MCCB Superior series has exceptional performance characteristics at the
rated breaking current of 50KA. This includes:
• Limiting short-circuit current, lp, to 106KA (maximum peak let-through
current)
As a result, the peak short circuit current (lp) is limited to the cut-
off current (Ic). This leads to a substantial reduction in electrodynamic
stresses in the overall system. l 2 let-through (proportional to the
shaded area) is considerably reduced, resulting in lower thermal
stresses in down-stream equipment and connecting cables.
4
The Superior Series MCCB
an in-depth look
Features
1 1 BMC material for
2 2 Arc chute
3 Mounting for ST or
5 Moving contacts
5
6 Clear and IEC-
6 7 compliant markings
9 Compact size
9
a b d i
c Features
a Arching chamber
b BMC
c Handle
e BMC
f Tripping mechanism
g Moving contact
h Fixed contact
i Thread nut
h g f e
5
The Technology of Tripping Devices
Materials (diagram 4)
The base and cover of the MCCB are made of a specially formulated
material, i.e. bold moulded compound (BMC). It has a high-impact thermal
strength, fire resistant and capable of withstanding high electromagnetic
forces that occur during a short-circuit. Majority MCCB manufacturers in the
market use pheonolic compounds with less electrical and mechanical
strength.
6
The Technology of Tripping Devices
Instantaneous Operation
If the overcurrent is excessive and the magnetization of the solenoid coil
strong enough to attract the armature, an instantaneous operation will
actuate the trip bar.
Instantaneous Operation
If the overcurrent is excessive, the armature is instantly attracted without the
influence of the moving core.
7
Tripping Characteristics
10 ≤ In ≤ 63 1 1 10In + 20%
Table A
5In + 20%
100 ≤ In ≤ 800 2 2
10In + 20%
10 ≤ In ≤ 63 2 2 12In + 20%
8
Installation and Fittings
Further adjustments are unnecessary or allowed for the circuit breaker or its
accessories during service as their settings have been fine tuned by LKE Electric.
The handle of the circuit breaker has three positions which will indicate when
the breaker is closed, opened or tripped respectively. When the handle is at the trip
position, it must be pulled backward first so as to reset the breaker and be ready
for closure.
If the security seal of the circuit breaker is kept intact for 24 months from the
delivery date, and instructions are followed for its storage and maintenance, any
inherently defective product will be repaired and/or replaced at no further expense
to the customer.
Hex. socket head screw M10 c/w terminal bar 22.5 - 37.2
Hex. socket head screw M12 c/w terminal bar 40.2 - 65.7
9
Arc Quenching Distance
Due to the unique design of the arc chute with an Arc Top Plate, the arc quenching
level is very low compared to other conventional models.
Arc Quenching
Model Code
Distance A & B (mm)
LKS-63C 15
LKS-63S
LKS-100C 20
LKS-100N
LKS-100S
LKS-100H
50
LKS-225C
LKS-225N
LKS-225S
LKS-225H 60
LKS-400C
LKS-400S
LKS-400H
LKS-600S
100
LKS-600H
LKS-800S
LKS-800H
measurements are in millimeter (mm)
10
How to select a proper MCCB for protection
It is very important to select and apply the right MCCB for a long lasting and
trouble-free operation in a power system. The right selection requires a detailed
understanding of the complete system and other influencing factors. The factors
for selecting a MCCB are as follows:
1 ) nominal current rating of the MCCB 2 ) fault current Icu, Ics
3 ) other accessories required 4 ) number of poles
Nominal Current
To determine the nominal current of a MCCB, it is dependent on the full load
current rating of the load and the scope of load enhancement in future.
11
Quick & Wide Selection Guide
The Superior series current limiting MCCB is available in 8 frame sizes, with ratings from 10A to 800A. Each
frame size offers several interrupting capacities (Icu), up to 65kA, at AC 415V. Available in C, N, S and H
configurations for various breaking capacity, the space-saving current limiting MCCB Superior series provides
greater design flexibility than before. The C and N configurations are for general use in a general circuit. A best-
seller worldwide, the C and N ranges from 60A to 800A in frame sizes. Also for general usage, the S and H
configurations have a higher interrupting capacity, from 15A to 800A in frame sizes, is actually an upgrade from
the C and N range.
Symmetrical 5 15 18 35 50 65
10
15
20
30 LKS-63C LKS-63S
40
LKS-100C LKS-100N LKS-100S LKS-100H
50
60
75
Breaker Rated Current (A)
100
125
150
160
LKS-225C LKS-225N LKS-225S LKS-225H
180
200
225
250
300
LKS-400S LKS-400H
315
400
500
LKS-600S LKS-600H
600
700
LKS-800S LKS-800H
800
12
MCCB – Electrical & Mechanical Features
LKS-63 LKS-100
Model Code
C S C N S H
Rated Voltage
Ue 415 415
(V), 50 Hz
P Poles 3 3
Electrical Characteristics
Weight
kg 0.9 1.6
(3 pole)
Characteristics
Mechanical
a 75 90
a c
c
mm b b 130 155
c 68 68
13
LKS-225 LKS-400 LKS-600 LKS-800
C N S H S H S H S H
3 3 3 3
125, 160, 180, 200, 225 250, 315, 350, 400 500, 600 700, 800
18 35 50 65 50 65 50 65 50 65
9 18 25 33 25 33 25 33 25 33
18 35 50 65 50 65 50 65 50 65
– – available available
14
Outline Dimensions of the MCCB
LKS-63 C, S LKS-100 C, N, S, H
LKS-225 C, N, S, H LKS-400 S, H
LKS-600 S, H LKS-800 S, H
15
Operating Characteristics & Ambient Compensation
LKS-63 C, S LKS-100
C, N, S, H
LKS-225 LKS-400 S, H
C, N, S, H
LKS-600 S, H LKS-800 S, H
16
Internal Accessories
Undervoltage release
Shunt release
Configurations: 1 NO + 1 NC
Alarm switch 2 NO + 2 NC
17
External Accessories
Insulation Barrier
The insulation barrier should be utilized on the MCCB to facilitate
termination of cable links. Used on the incoming side of the MCCB, it
provides additional safety as it is made of superior insulating materials
that have good mechanical and electrical properties. The insulation
barrier prevents accidental contacts and flash-over between each
phase and is highly recommended for the breakers especially during
installation of a switchboard.
18
Internal Accessories Specification
Shunt Trip
Circuit Breaker > 400A Circuit Breaker > 225A Circuit Breaker > 400A Circuit Breaker > 225A
2 NO + 2 NC 1 NO + 1 NC 2 NO + 2 NC 1 NO + 1 NC
Auxiliary Contact
Frame Size 100A < In < 630A 100A < In < 630A
I/Ic 10 10
Make U/Uc 1 1
Cos ø 0.3 0.3
I/Ic 1 1
Category
Break U/Uc 1 1
AC-15 0.3 0.3
Cos ø
19
Installation and Fittings
External Accessories
20
Outline Dimensions of Rotary Handle & Door Hole
Shortest Distance between Hinge &
Outline & Mounting Drawing
Handle Center and available Shaft Space
Features
• can be pad-locked in both ON and OFF positions.
• when door is locked in ON position, can be opened in OFF position.
• protective class (based on IEC529 standards) at IP54.
21
Selection Table & Installation Guide for Accessories
Name of Accessory LKS-63 LKS-100 LKS-225 LKS-400 LKS-630
LKS-800
Alarm Switch
* Trip Indication
Auxiliary Switch
* On & Off Indication
Shunt Trip
* Remote Trip Unit
UVT
* Undervoltage Release
2 Auxiliary Switch
Auxiliary + UVT
Alarm + UVT
item symbol
Left Side Right Side
1. Only lead wire type is available Alarm
* 2. For Alarm, Auxiliary, Switch and UVT,a module is
* mounted externally on the cover.
Auxiliary switch
Shunt trip
MCCB On/Off Toggle UVT
22
Outline Drawings of Accessories
Shunt Trip Release Model Code A B C D
ACMSST - 63 39 31 42 23.5
ACMSAL - 630 55 63 28 39
ACMSAX - 630 55 63 28 39
ACMSAA - 630 55 63 28 39
24
Outline Drawings of Accessories
Motor Operating Mechanism Model Code A B C
ACMRH - 50 100 25 49 68
25
Outline Drawings of Accessories
Plug-in Kit
MZ1-100/30 MZ1-225/30 MZ1-400/30 MZ1-630/30
model code
A1 60 70 44 140
B 30 38 50 58
B1 70 73 135 143
D 6 6 10 10
D1 0 10 13 13
E1 0 26 32 0
F 60 70 87 140
F1 M10 25 28 44
G 13 13 18 17
H 26 34 40 53
H1 16 15 24 20
J M10 6 8 11
K 14 17.5 27 27
L1 60 70 87 140
M M5 M5 M8 M8
m 0 108 120 0
m1 62 79 79 146
m2 122 134 0 0
N 0 18 15 15
26
Definition of Short-circuit
and Short-circuit Current
Short-circuit in a Network
When a short-circuit in a network occurs, it will create a highly damaged and
abnormal condition to the system, whereby the normal insulation of the system, be
it the cables or equipment and load, are damaged.
The function of the MCCB as a protection device, is to protect overloads and
bring the effect of this faulty condition under control at a fast speed in order to
reduce the damages.
The LKE Superior series MCCB, with the right combination of accessories and
proper selection to coordinate between the down-stream and up-stream of the
rated current and fault level, is one of the more reliable circuit breaker protection
device available.
It is important to understand the full load current and fault level to determine
the rated current and short-circuit kA of the MCCB before selecting the right
MCCB to protect the down-stream cable, equipment and load.
The value of the short-circuit current at a fault-junction depends mainly on:
• the kVA of the supply source, (either a transformer or generator).
• the type of supply system.
• the length and cross section of the cable and device lying in between the
source of supply and fault-junction.
Types of Short-circuit
Before calculating the short-circuit current at any point of the network, one
must be able to differentiate the various types of short-circuit. In a three-phase
network, short-circuits are generally classified as below, depending on the number
of conductor affected and with or without fault-to-earth.
27
The Peak Value of the Short-circuit Current
When an R-L series circuit is closed with an A/C source, the current
component results in:
1 ) an A/C component with a phase shift with respect to the voltage
2 ) a D/C decaying component.
The arc component is superimposed on the D/C component. The initial peak
value of the short-circuit current depends on the voltage at the instance of the
breaker closing. The two extreme cases are:
a ) when the breaker is closed at peak voltage, the D/C component is zero and
the fault current is symmetrical or balanced.
28
Determination of the Fault Current
The initial peak value depends on the instance of the breaker closing and on the
factor “K = R/X” [Refer Fig.1]. In practical applications, the value of “K” lies mostly
between 1.1 to 1.5. The electro-dynamic stress on the current carrying parts
depends on this peak value “Ip”.
Isc = In x 100/Z
where,
Isc - short-circuit current ( A )
In - rated current of the transformer (Full load current)
Z - percentage impedance of the transformer
In this example, the short-circuit current close to the transformer is ~28 kA. The
breaking capacity of the MCCB installed at this point must be higher than this
value. This is applicable if a high breaking capacity MCCB with an ultimate short-
circuit breaking capacity Icu = 35 kA or 50 kA is used here. It is immaterial whether
the simple formula used above is sufficiently accurate or not. The selected circuit
breaker will have enough capacity in reserve.
The short-circuit current calculated above can also be read out from the table
“Rated and short-circuit currents of 3-phase standard transformers” (refer to
page 30).
29
Determination of the Fault Current
at Transformer Terminal
Rated and Short-circuit Currents of 3-phase Standard Transformers at Secondary Terminal.
50 70 1391
30
Calculation of the Short-circuit Current in a Supply System
In a supply system, the further away from the transformer, the higher the
impedance. As such, the lower the value is for the short-circuit current. Each length
source of conductor or device in the circuit provides an impedance which reduces the
short-circuit current. To calculate the maximum level possibility of the short-circuit
current, all the impedances lying between the transformer and the MCCB must be
considered, be it with formula or simple diagram.
8 50 35 25 16 10 6 4
12 70 50 35 25 16 6
15 95 70 50 35 25 16 10
20 120 95 70 50 35 25 16 10
30 120 95 70 50 35 25 16
45 185 150 120 95 70 50 35 25
60 150 120 95 70 50 35
80 185 150 120 95 70 50 35
120 120 95 70 50
150 120 95 70
31
Protection for Generators
32
Protection of Motor by Breakers
The IEC standard classifies the coordination of the breaker and contactor into
the following 3 categories for damages on the contactor when a fault occurs on
the load side:
Category A – coordination is when the magnetic contactor is damaged to the
extent that it will require replacement. Other major components
may also require replacement or complete assembly.
Category B – coordination is when repair requirements are only to the
component parts, due to welding of contacts or melting of the
thermal relay heater.
Category C – a perfect coordination is achieved when no damages are
sustained by the contactor.
Selection Principle
1. The MCCB current rating should be higher than the motor full load current.
2. The motor starting current and starting time should be below the minimum
time/current curve of the MCCB. A margin of about 50% should be allowed for
the starting time to allow for the voltage drop or increase of a mechanical load
friction.
3. The MCCB magnetic trip current should be 1.4 to 1.7 times the motor rated
starting current ( lock-rotor current).
4. For star- delta or auto-transformer starters, the MCCB magnetic trip should be
at least 2 to 2.4 times the motor rated starting current (or lock-rotor current).
33
Selection Guide
Capacitance Load
The capacitors must be able to withstand a continuous overload of 30% due
to the harmonic currents. As a result, the circuit breaker must be derated b 30%.
12.5 18 25
20 29 40
30 44 63
50 72 100
75 110 160
90 132 200
150 10.0 + j18.07 27.4 + j164.4 8.341 + j16.57 300 1.44 3.27
300 4.8 + j10.9 13.7 + j82.2 3.914 + j9.773 1000 1.22 5.21
34
Selection Guide
Impedance of Electric Cable
50Hz 60Hz
Cable Rw
(mm2) (mΩ/m) 2-core, single core, single core 2-core, single core, single core
3-core closed 6cm distance 3-core closed 6cm distance
NOTE: The resistance values are based on JIS C3307 660V grade polyvinyl chloride insulated and vinyl sheathed cable (w).
The reactance value L = 0.05 + 0.4605 log10 D/r (m/H/km)
(D = core center to center distance, then Xw = 2.π fl x 10 -3 (mΩ/m), f = frequency was calculated).
35
Selection Guide
Impedance of Bus Duct (Zb)
Reactance (mΩ/m)
Rated Current Resistance
(A) (mΩ/m)
50Hz 60Hz
36
Selectivity
What is Selectivity?
Selectivity between 2 protective devices in series, such as the MCCB1
& MCCB2, is also called discrimination. The purpose of selectivity is to
coordinate the 2 circuit breakers in cascade, eg. A and B (see diagram). This
means only the B breaker trips in case of fault occurring at C and a
continuous supply of power to the remaining loads through the A breaker.
Current Selectivity
This technique is commonly used in low tension switchboards,
Diagram 3
achievable by adjusting the tripping unit current setting. For 2 breakers in
series, the pick-up current on the upstream breaker is set to a value higher
than the prospective short circuit current at the point of the fault junction of
the down stream breaker.
This selectivity technique is used particularly for links between main
boards and secondary boards.
37
LKE’s Low & Medium Voltage
Range of Products
LK-VB1
LK-GLBS Vacuum Circuit Breaker
SF6 Load Break Switch
LK-LTPM
SF6 Ring Main Unit
LK-LBS
Compressed Air
Load Break LK-LTHO
Switch SF6 Pole-Mounted
Switch Disconnector
LK-VLBS
Vacuum
Load
Break
Switch
LK-CUBIC
Low Voltage
Switchboard
LK-LCA LK-ATS
Compressed Air Auto Transfer
Ring Main Unit Switch
LK-LCA LK-ACB
SF6 Ring Main Unit Air Circuit Breaker
capacity of products range from 380VAC – 36kV and rated current from 5A – 6300A
OPTIMAL SOLUTIONS
SUPERIOR QUALITY
I N S TA N T D E L I V E R Y
info@lke-electric.com
www.lke-electric.com