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EntelliGuard* L

Applications

Protection of generator sets, motors, capacitor banks and Remark
transformers Furthermore, the prevention of anomalies as the motor losing a
Use of EntelliGuard Breakers in Automatic Power Transfer phase or a motor with blocked rotor need to be prevented and
Systems (ATS) require additional protection devices.
Next to the ‘Standard’ protection devices, the EntelliGuard
Introduction Electronic Trip Unit has a thermal memory function, an optional
The electronic trip unit used in the EntelliGuard Air Circuit Breaker 3 phase undervoltage relay and current unbalance device, thus
offers many additional protection devices. Here number of the providing comprehensive motor protection.
possible applications of these devices are described briefly.

Protection of generator sets Protection of capacitor banks
The overload and short-circuit devices used to protect a Air Circuit Breakers are designed to offer high making and
generator need to react quicker and at lower current levels than breaking capacities under adverse conditions: The switching
those used to protect other devices. of capacitor banks has little to no effect on the breaker, its
characteristics as a protective device or on its lifespan.
After establishing, the capabilities of the generator are set under
overload and short-circuit conditions. The protection devices However the current flowing in the circuit can trip a circuit Applications
need to be adjusted accordingly. breaker and a capacitor load does display certain anomalies.
Here the current flowing in the circuit cannot be assumed to
On a Air Circuit Breaker use of the ‘faster’ overload be the calculated capacitor current only. The effective current
protection bands (LTDB set between minimum and the C6 band) value is higher due to harmonic content (normally assumed
and a low setting of the timed short-circuit protection (2.5 x Ir) is as 30%) and an allowance must be made for tolerances in the
recommended. The optional 3 phase undervoltage protection capacitance of the units (10%). The protection devices of the Intro
available in the GT-H trip unit can also be considered. Air Circuit Breaker must be set accordingly.

Protection of motors Protection of LV / HV transformers A
On starting, electrical motors draw more current than when Transformers generally produce a very high inrush current.
running under normal conditions. These starting currents differ The crest values of the first half cycle may reach values of
strongly per type and should not cause tripping of the device 15 to 25 times the normal rated current. B
protecting the circuit. Manufacturers data and tests have indicated that, a protection
The IEC60947-4 has defined four different ‘Operational’ or ‘Trip’ device feeding a transformer must be capable of carrying the
classes: following current values without tripping.
C

Trip class Required tripping times at Transformer Crest inrush values
value
1.2 x In 1.5 x In 7.2 x In 1st period 2nd period After 3 periods
10A t < 2 hours t < 2 min. 2 ≤ t < 10 sec. < 50 kvA 25 x In 12 x In 5 x In D
10 t < 2 hours t < 4 min. 4 ≤ t ≤ 10 sec. ≥ 50 kvA 15 x In 8 x In 3,5 x In
20 t < 2 hours t < 8 min. 6 ≤ t ≤ 20 sec.
30 t < 2 hours t < 12 min. 9 ≤ t ≤ 30 sec.
It is recommended that the timed short-circuit device of a Air E
This table is in some cases extended to include a ‘Trip class 40’ Circuit Breaker is set to at least 8 x Ir with a time delay of 30
(assumed to be a 15-40 second band at 7.2 x In). milliseconds (STDB band 1). If an instantaneous protection
On a Air Circuit Breaker, use of the ‘slower’ protection bands device is present, the use of the extended adjustment range X
that closely match the indicated classes is recommended (LTDB with setting of 20 x Ie is advisable (=15 x In plus tolerances).
set between the C8 to the C22 band).

Switching on a motor also produces a high but very short Automatic Transfer Systems (ATS)
inrush peak current which could activate the short-circuit EntelliGuard Air Circuit Breakers are available with mechanical
protection of a breaker and cause unexpected tripping. Here interlocks for 2 to 3 breakers and have a unique electrical
the timed short-circuit device of a Air Circuit Breaker must be network interlocking system allowing the user to completely
set to at least 12 x Ir with a time delay of 50 milliseconds (STDB lock out one or more breakers.
band 3). If an instantaneous protection device is present and The logical transfer of power from one source to another
switched on, a setting of at least 12 x Ie is recommended. is thus strongly simplified whilst the high speed electrical
closing and opening of the device allows their use in
After an overload event, if motor and wiring are still warm, a synchronization applications.
immediate re-energization of the electrical circuit could result
in damage of the electrical circuit and the motor. Here, numerous other EntelliGuard protection features can
be used, one of which being the Electronic Trip unit 3 phase
The overload protection device must incorporate a thermal undervoltage release. This is to establish if voltage on a
memory device that prevents re-energization before a certain certain power source is present and if a generator set has
cooling time has elapsed. reached its nominal voltage.

D.7