Ground-Fault Protection (G or ANSI 50N-TD/51N)

Presentation

Ground-fault protection provides protection against phase-to-ground fault, which is more sensitive than protection based on phase current only. It is generally used in TN-S systems but could also be used in other earthing systems.

A ground-fault in the protection conductors can cause local temperature rise at the site of the fault or in the conductors.

Ground-fault and neutral protection are independent and can therefore be combined.

Ground-fault protection is based on the summation of the phases and neutral current. It detects faults downstream of the circuit breaker.

Availability

Ground-fault protection is available on:

• TS 6.0 S trip system.

• 3-pole and 4-pole circuit breakers

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External Neutral Current Transformer (ENCT) can be used to measure the current on neutral. The commercial references of the compatible ENCT are: 33576, 34035, 34036. For information about the installation of ENCT, refer to the ENCT Instruction Sheet - 48049-222-04, and 48049-273-04.

Ground-fault protection is powered by the current flowing through the internal current transformers of the circuit breaker and it does not require an additional external power supply.

Operating Principle

The ground-fault current is calculated or measured according to the circuit breaker configuration, as shown in the following table.

The ground-fault protection pickup Ig sets the level of ground-fault current at which the circuit breaker trips when reaching the ground-fault protection time delay tg.

The time delay tg sets the length of time during which the circuit breaker carries a ground-fault within the ground-fault protection pickup Ig range.

The time delay tg can be adjusted to:

• Seven setting values with I²t on. In this case, the tripping curve is an inverse time curve up to 2 x Ir, meaning that the time delay decreases as the current increases. Above 2 x Ir, the tripping curve is a definite time curve with a constant tripping time.

• Seven setting values with I²t off. In this case, the tripping curve is a definite time curve with a constant tripping time.

Ground-fault protection is based on the true RMS current of phases and neutral.

In order to trip on an intermittent electrical fault, the trip system accumulates the intermittent currents in the ground-fault tripping range that do not last long enough to trigger a trip. This accumulation leads to shorter tripping times than those set.

Setting the Protection

The ground-fault protection settings are:

• Ig: ground-fault protection pickup

• tg: ground-fault protection time delay

• I²t (tg): ground-fault protection curve (I²t on or I²t off)

They can be set by using the Ig and tg rotary switches on the front face of the TS trip system.

Setting the Ig Pickup

The Ig pickup setting value is expressed according to the rated current In.

Ig pickup = Ig setting x In rated current.

The Ig setting values are: A, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1, and off.

• when In < 3200 A, A = 0.2

• when In ≥ 3200 A, A = 500 A

Setting the tg Time Delay

Testing the Ground-Fault Protection

Test the operation of ground-fault protection as follows:

1. Check that the circuit breaker is closed.

2. Use a thin screwdriver to briefly push in (< 1 s) the TEST button on the front face of the TS trip system.

3. The circuit breaker trips.

4. If the circuit breaker does not trip, contact your Schneider Electric Services representative.

Predefined Events

Predefined events cannot be modified by the user. For general information about events, refer to Event Management.

Recommended Actions

Resetting a Trip Event

For information about resetting the circuit breaker after a trip due to an electrical fault, refer to the relevant document:

• EasyPact MVS1 Circuit Breakers with TS Trip System - User Guide
• EasyPact MVS2 Circuit Breakers with TS Trip System - User Guide