Ground-Fault Protection

Presentation

Ground-fault protection on MicroLogic 6 trip units protects all types of electrical distribution applications against ground-fault currents in the TN-S system.

For more information on ground-fault currents, refer to DOCA0140EN ComPact NSX - Circuit Breakers and Switch-Disconnectors 100–630 A - User Guide.

Operating Principle

Ground-fault protection is definite time:

It includes the possibility of an I²t inverse time curve function.
Set as Ig pickup and as tg trip time delay.

The ground-fault protection settings are:

Ig: ground-fault protection pickup
tg: ground-fault protection time delay
I²t: ground-fault protection I²t curve in ON or OFF position

Setting the Ground-Fault Protection

Set the Ig pickup:

With the MicroLogic 6 trip unit Ig dial to preset the value and with the keypad to fine-tune the value
With EcoStruxure Power Commission software (password-protected)
By sending a setting command using the communication network (password-protected)

Set the tg time delay:

With the keypad on the MicroLogic 6 trip unit
With EcoStruxure Power Commission software (password-protected)
By sending a setting command using the communication network (password-protected)

The tg time delay setting includes activation/deactivation of the I²t function.

Ig Pickup Setting Values

The Ig pickup setting value is in multiples of In.

The default Ig pickup setting value is the same as the minimum value read on the dial:

0.40 x In for trip units rated 40 A
0.20 x In for trip units rated > 40 A

Ground-fault protection can be deactivated by setting the Ig dial to the OFF position.

Ground-fault protection can be reactivated even with the Ig dial in the OFF position:

By fine-tuning on the keypad
With EcoStruxure Power Commission software (password-protected)
By sending a setting command using the communication network (password-protected)

The following two tables specify the setting values (preset by a dial) and setting ranges (set on the keypad.)

On the keypad, the increment is 0.05 x In.

For trip units rated 40 A

Type of setting	Value or setting range (x In)
Preset by a dial	0.40	0.40	0.50	0.60	0.70	0.80	0.90	1	OFF
Setting range on the keypad	0.40	0.40	0.4–0.5	0.4–0.6	0.4–0.7	0.4–0.8	0.4–0.9	0.4–1	0.4–1 + OFF

For trip units rated > 40 A

Type of setting	Value or setting range (x In)
Preset by a dial	0.20	0.30	0.40	0.50	0.60	0.70	0.80	1	OFF
Setting range on the keypad	0.20	0.2–0.3	0.2–0.4	0.2–0.5	0.2–0.6	0.2–0.7	0.2–0.8	0.2–1	0.2–1 + OFF

The accuracy range is +/-10%.

tg Time Delay Setting Values

The tg time delay setting value is in seconds. The hold and breaking times are in milliseconds.

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

The following table shows the setting values of tg time delay in seconds (s) with the I²t function active (I²t ON) or not active (I²t OFF). The associated hold and breaking times are shown in milliseconds (ms):

Function	Setting value
tg with I²t OFF (s)	0	0.1	0.2	0.3	0.4
tg with I²t ON (s)	–	0.1	0.2	0.3	0.4
Hold time (ms)	20	80	140	230	360
Maximum breaking time (ms)	80	140	200	320	500

I²t Inverse Time Curve Function

The I²t inverse time curve function for ground-fault protection operates in the same way as the I²t inverse time curve function for short-time protection.

Testing the Ground-Fault Protection

The ground-fault protection can be tested to check the electronic tripping function of the trip unit. Use the keypad of the MicroLogic 6 trip unit to perform this test.

The ground-fault protection test can be performed with the padlock locked or unlocked .

Follow these steps to test and reset the ground-fault protection on MicroLogic 6 trip units.

Step	Action	Display
1	Provide a power supply to the trip unit so that the screen displays the result of the test after the circuit breaker trips.	–
2	Select the Instantaneous measurement readout mode (the display is the most heavily loaded phase, in this example Phase 2).
3	Select the ground-fault current measurement screen (the value is a percentage of the Ig setting).
4	Access the ground-fault protection test function by pressing OK. The tESt pictogram appears and the OK pictogram blinks.
5	Prompt the ground-fault protection test by pressing OK. The circuit breaker trips. The ground-fault protection trip screen is displayed.
6	Acknowledge the ground-fault trip screen by pressing OK. The Reset? OK pictogram blinks.
7	Confirm by pressing OK again. The confirmation OK displays for 2 s.