LV Air Circuit Breakers – (Typical Specifications)

1. General
(a) LV Air circuit breakers shall comply with standards IEC 60 947-1 and 2 or standards derived from the latter.
(b) The Air circuit breakers shall have a breaking capacity justified by calculations taking into account their installation location.
(c) The number of circuit-breaker poles shall be as indicated on the single-line diagram.
(d) The Air Circuit Breaker should be available from 800 Amps to 4000 Amps in only one Frame size.
2. Construction
2.1. General
(a) Circuit breakers shall be designed in such a way that maintenance may be carried out as a function of their use. To reduce maintenance, electrical endurance shall be greater than 12 500 cycles up to 1600 A, 10 000 cycles up to 4000 A and 5000 cycles for values greater than 4000 A.
(b) No safety clearance shall be required around drawout circuit breakers. For fixed circuit breakers, 150 mm of free space shall be provided above the arc chutes to allow removal of the latter.
(c) The operating mechanism shall be of the Open/Closed/Open stored-energy type. The closing time shall be less than or equal to 70 milliseconds.

2.2. Main contacts
(a) The main contacts shall be designed such that no maintenance shall be required under normal conditions of use.
(b) The main contacts shall be equipped with a visual wear indicator that may be accessed by removing the arc chutes, for immediate assessment of contact wear without requiring measurements or specific tools.

2.3. Arc chutes
(a) The arc chutes shall be removable on site.
(b) They shall be equipped with metal filters to reduce effects perceptible from the outside during current interruption.

2.4. Connection/disconnection mechanism
(a) It shall be possible to disconnect the circuit breaker without having to open the door. The three possible positions (connected, disconnected and test) shall be indicated.
(b) Before carrying out a disconnection or connection operation, the operator shall be required to press a release button located on the front of the chassis.
(c) The door shall be equipped with a locking system preventing door opening with circuit breaker in the connected position. Safety shutters shall be placed over the main incoming and outgoing circuits. A mismatch-prevention system shall block insertion of a drawout circuit breaker with a power rating greater than that of the fixed part.

2.6. Electrical auxiliaries
(a) All electrical auxiliaries, including the spring-charging gear motor, shall be installable on site without requiring adjustments or any tools other than a screwdriver.
(b) The auxiliaries shall be placed in a compartment which, under normal operating conditions, shall not contain any conducting parts capable of entering into electrical contact with the circuit-breaker poles. It shall be possible to connect all auxiliary wiring from the front of the circuit breaker.

2.7. Mechanical indicators
Mechanical indicators on the front panel of the power circuit breakers shall indicate the following status conditions:

1. "ON" (main contacts closed) Spring charged
2. "ON" (main contacts closed) Spring discharged
3. "OFF" (main contacts open) Spring charged – circuit breaker ready to close
4. "OFF" (main contacts open) Spring charged – circuit breaker not ready to close
5. "OFF" (main contacts open) Spring discharged

3. Protection / Control unit
3.1. General
(a) The control unit shall be interchangeable on site for adaptation to changes in the installation.
(b) Sensors shall be non-magnetic or of the Rogosky type for accurate current measurements.
(c) The control unit shall measure the true rms value of the current.
(d) The control unit shall comprise a thermal memory to store temperature-rise data in the event of repeated overloads or earth faults.

3.2. Protection
The control unit shall offer the following protection functions as standard:
(a) Long-time (LT) protection with an adjustable current setting and time delay;
(b) Short-time (ST) protection with an adjustable pick-up and time delay;
(c) Instantaneous (INST) protection with an adjustable pick-up and an OFF position.

(d) Current and time-delay settings shall be indicated in amperes and seconds respectively on a digital display.
(e) Earth-fault protection with an adjustable pick-up and time delay shall be provided if indicated on the appended single-line diagram.

3.3. Measurements
(a) An ammeter with a digital display shall indicate the true rms values of the currents for each phase.
(b) A LED bargraph shall simultaneously display the load level on the three phases.
(c) A maximeter shall store in memory and display the maximum current value observed since the last reset. The data shall continue to be stored and displayed even after opening of the circuit breaker.
3.3 Power measurements
(a) The control unit shall measure voltages and calculate power and energy values.
(b) These values shall be displayable on the screen and updated every second. The minimum and maximum values shall be stored in memory.
(c) Accuracy
 Energy (kWh) 2.5%
 Real power (kW) 2.5%
 Apparent power (kVA) 2.5%
 Demand power (kWh) 2.5%


3.4Measurement of power quality
The control unit shall offer functions allowing the analysis of the quality of AC distribution system power, including:
 Measurement of the amplitude and phase of current and voltage harmonics up to the 50th order;
 Measurement of the fundamental components of the voltage, current, active power, reactive power and apparent power;
 Measurement of total current and voltage harmonic distortion.

3.5 Additional protection functions
The control unit shall offer the protection functions listed below.

Threshold Time delay
Minimum voltage
Maximum voltage
Voltage imbalance 25 to 690 V
100 to 931 V
10 to 90% Umean 0.5 to 3s
0.25 to 1 s
1 to 15 s
Minimum frequency
Maximum frequency 33 to 400 Hz
33 to 540 Hz 0.5 to 3 s
0.25 to 1 s
Current imbalance
Maximum current 5 to 90% Imax
0.4 In to Isd 1 to 15 s
0.5 to 1000 s
Phase sequence * 1/2/3
Instantaneous
Reverse power 2 to 20% of Pn 0 to 20 s

3.6 Communication
The circuit breaker shall be capable of communicating the following data via a bus:
 Circuit-breaker status (open/closed, connected/disconnected/test, tripped on a fault, ready to close);
 Control-unit settings;
 Tripping causes;
 The measurements processed by the control unit: current, voltage, frequency, power, power quality.
 It shall be possible to remotely control the circuit breaker.
 It shall be possible to remotely modify circuit-breaker settings:
 Settings within the range defined by the switches on the front panel of the control unit;
 Settings of the protection functions and the alarms.
 Communications functions shall be independent of the control unit.

3.7Maintenance
 The last ten trips and alarms shall be stored in two registers that may be consulted locally (date and time, type of fault or alarm).
 Maintenance indicators shall be displayable on request on the front panel:
 Percent wear of contacts;
 Operations counter.

4.End of service life
 The manufacturer shall provide instructions on the removal, dismantling and processing of circuit-breaker materials at the end of service life (material composition, weight, toxicity).