Ground-Fault Protection (G or ANSI 50N-TD/51N) - MicroLogic Active User Guide

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.

NOTE: Ground-fault protection is also called earth-fault protection.

Ground-fault protection is based on the summation of the phase and neutral currents.

Availability

Ground-fault protection is available on:

MicroLogic Active 6.0 control units for IEC standard
3-pole and 4-pole circuit breakers

An External Neutral Current Transformer (ENCT) can be used to measure the current on neutral. For information about the installation of ENCT, consult the instruction sheet on the Schneider Electric website: NHA14388

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.

NOTE: When ENCT is not used, short circuit terminals T1 and T2.

Operating Principle

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

Circuit breaker configuration	Ig ground-fault current
3P	Ig = I1 + I2 + I3
4P	Ig = I1 + I2 + I3 + IN
3P + ENCT	Ig = I1 + I2 + I3 + IN (ENCT)

The ground-fault protection threshold 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 threshold Ig range.

The time delay tg can be adjusted to:

Four 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.
Five 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, up to harmonic 15.

In order to trip on an intermittent electrical fault, the control unit 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

Ground-fault protection can be enabled or disabled with EcoStruxure Power Commission software.

The ground-fault protection settings are:

Ig: ground-fault protection threshold
tg: ground-fault protection time delay
I²t (tg): ground-fault protection curve (I²t ON or I²t OFF)

They can be set as follows:

On the MicroLogic Active PIN code-protected display screen, by pressing the Protection Settings button, and selecting the G (ground-fault protection) area. See Protection Setting Procedure.
With EcoStruxure Power Commission software (password-protected)
With EcoStruxure Power Device app (password-protected)

Two modes of configuring the protection settings are available:

Quick setting mode is used to configure quick protection settings
Fine adjustment mode is used to configure fine protection settings

Quick Protection Settings

Quick protection settings are available:

On the MicroLogic Active HMI
With EcoStruxure Power Device app

Ig setting for MicroLogic Active 6.0 IEC standard

Setting	Unit	Values	Factory setting	Accuracy
Ig for In ≤ 400 A	A	(0.3 / 0.4 / 0.5 / 0.6 / 0.7 / 0.8 / 0.9 / 1) x In	0.3 x In	+/– 10%
Ig for In > 400 A, excluding 1,250 A	A	(0.2 / 0.3 / 0.4 / 0.5 / 0.6 / 0.7 / 0.8 / 0.9 / 1) x In	0.2 x In	+/– 10%
Ig for In = 1,250 A	A	(0.2 / 0.32 / 0.4 / 0.48 / 0.6 / 0.72 / 0.8 / 0.88 / 1) x In	250 A	+/– 10%

tg setting for MicroLogic Active 6.0 IEC standard

Setting	Unit	Setting Value
tg with I²t OFF	s	0	0.1	0.2	0.3	0.4	0.6	0.8	1.0
tg with I²t ON	s	–	0.1	0.2	0.3	0.4	0.6	0.8	1.0
Non-tripping time	s	> 0.02	> 0.08	> 0.14	> 0.23	> 0.36	0.55	0.71	0.9
Maximum breaking time	s	< 0.08	< 0.14	< 0.20	< 0.32	< 0.50	0.63	0.8	1.0

The default tg time delay setting value is 0 s with I²t OFF.

NOTE: When tg is set to 0 s and I²t is changed to ON, the tg time delay is automatically set to 0.1.

Fine Protection Settings

Fine protection settings are available:

On the MicroLogic Active HMI
With EcoStruxure Power Commission software
With EcoStruxure Power Device app

Ig setting for MicroLogic Active 6.0 IEC standard

Setting	Unit	Range	Step	Factory setting	Accuracy
Ig for In ≤ 400 A	A	0.3–1 x In	1 A	0.3 x In	+/– 10%
Ig for 400 A <In ≤ 1,000 A	A	0.2–1 x In	1 A	0.3 x In	+/– 10%
Ig for In > 1,000 A	A	0.2–1 x In	10 A	0.3 x In	+/– 10%

tg setting for MicroLogic Active 6.0 IEC standard

Setting	Unit	Setting Value
tg with I²t OFF	s	0	0.1	0.2	0.3	0.4	0.6	0.8	1.0
tg with I²t ON	s	–	0.1	0.2	0.3	0.4	0.6	0.8	1.0
Non-tripping time	s	> 0.02	> 0.08	> 0.14	> 0.23	> 0.36	0.55	0.71	0.9
Maximum breaking time	s	< 0.08	< 0.14	< 0.20	< 0.32	< 0.50	0.63	0.8	1

Zone Selective Interlocking (ZSI)

The ZSI characteristics and external wiring of the zone selective interlocking function, are described specifically.

If ZSI IN is not set to 1 (open circuit between Z3 and Z4 terminals), the maximum breaking time is 0.08 s regardless of the tg setting value.

When ZSI IN is set to 1 and connected to the ZSI OUT of a downstream device (or when ZSI is not used, there is a jumper between the Z3 and Z4 terminals), the tg time delay is used.

The Ig threshold activates ZSI OUT (Z1 and Z2 terminals).

NOTE: MasterPacT MTZ circuit breakers are delivered with a jumper installed between Z3 and Z4.

Predefined Events for MicroLogic Active 6.0

The protection function generates the following predefined events:

Code	Event	History	Severity
0x4003 (16387)	Ground Fault (Ig) trip	Trip	High
0x0C09 (3081)	Ig protection disabled	Protection	Low
0x6203 (25091)	Ig start	Protection	Low

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

Protection events are generated as follows:

The start event is generated when the protection picks up.
The trip event is generated when the circuit breaker tripping voltage release (MITOP) activates.

Recommended Actions for MicroLogic Active 6.0

Code	Event	Recommended actions
0x4003 (16387)	Ground Fault (Ig) trip	Reset the circuit breaker. See Resetting a Trip Event.
0x0C09 (3081)	Ig protection disabled	No action required. For information only.
0x6203 (25091)	Ig start	No action required. For information only.

Protection Test for MicroLogic Active 6.0

The protection test function for MicroLogic Active 6.0 control unit simulates a trip generated by ground-fault protection.

Perform the protection test as follows:

Step	Action
1	Check that the circuit breaker is closed and the control unit is supplied with power (Ready LED is flashing).
2	Use the MicroLogic Active HMI to perform the protection test. The Ig test launched event is generated.
3	The circuit breaker trips. The Ig test trip event is generated.
4	If the circuit breaker does not trip, the Ig test - no trip event is generated. Restart the test. If the circuit breaker does not trip again, contact your Schneider Electric Services representative.

Protection Test Events for MicroLogic Active 6.0

The protection test function generates the following predefined events:

Code	Event	History	Severity
0x401E (16414)	Ig test trip	Trip	High
0x1413 (5139)	Ig test - no trip	Diagnostic	High
0x142A (5162)	Ig test launched	Diagnostic	Low

Recommended Actions for MicroLogic Active 6.0 Protection Test

Code	Event	Recommended actions
0x401E (16414)	Ig test trip	Reset the circuit breaker. See Resetting a Trip Event.
0x1413 (5139)	Ig test - no trip	Restart the test. If the circuit breaker does not trip again, contact your Schneider Electric Services representative.
0x142A (5162)	Ig test launched	No action required. For information only.

Resetting a Trip Event

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

MasterPacT MTZ1 IEC Circuit Breakers with MicroLogic Active Control Unit - User Guide
MasterPacT MTZ2/MTZ3 IEC Circuit Breakers with MicroLogic Active Control Unit - User Guide