Short-Time Protection

Presentation

Short-time protection on MicroLogic 5, 6, and 7 trip units protects all types of electrical distribution applications against short-circuit currents.

It is identical for MicroLogic 5, 6, and 7 trip units.

Operating Principle

Short-time protection is definite time:

It incorporates the possibility of an I²t inverse time curve function.
It is set using the Isd pickup and the tsd trip time delay.

The short-time protection settings are:

Isd: short-time protection pickup
tsd: short-time protection time delay
I²t: inverse time curve function (ON or OFF)

Setting the Short-Time Protection (MicroLogic 5)

Set the Isd pickup:

With the MicroLogic trip unit Isd dial to preset the value and 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 tsd time delay:

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

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

Setting the Short-Time Protection (MicroLogic 6 and 7)

Set the Isd pickup and tsd time delay:

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

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

Isd Pickup Setting Values

The Isd pickup setting value is in multiples of Ir.

The default Isd pickup setting value is 1.5 x Ir (minimum dial value).

The following table shows the setting values (preset by a dial) and setting ranges (set on the keypad) of the Isd pickup:

Type of setting	Value or setting range (x Ir)
Preset by a dial (MicroLogic 5)	1.5	2	3	4	5	6	7	8	10
Setting range on the keypad ⁽¹⁾ Increment: 0.5 x Ir	1.5	1.5–2	1.5–3	1.5–4	1.5–5	1.5–6	1.5–7	1.5–8	1.5–10
(1) For MicroLogic 6 and 7 trip units, the setting range value on the keypad is 1.5–10 x Ir.

Type of setting

Value or setting range (x Ir)

Preset by a dial (MicroLogic 5)

1.5

Setting range on the keypad ⁽¹⁾

Increment: 0.5 x Ir

1.5

1.5–2

1.5–3

1.5–4

1.5–5

1.5–6

1.5–7

1.5–8

1.5–10

(1) For MicroLogic 6 and 7 trip units, the setting range value on the keypad is 1.5–10 x Ir.

The accuracy range is +/-10%.

tsd Time Delay Setting Values

The following table indicates the setting values for the tsd 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
tsd with I²t OFF (s)	0	0.1	0.2	0.3	0.4
tsd with I²t ON (s)	–	0.1	0.2	0.3	0.4
Hold time (ms)	20	80	140	230	350
Maximum breaking time (ms)	80	140	200	320	500

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

I²t Inverse Time Curve Function

Use the I²t inverse time curve function to improve circuit breaker coordination. Use it when a protection device using inverse time only is installed downstream, for example a fuse protection device.

Example:

The following graphs illustrate an example of selective coordination between a ComPacT NSX630 circuit breaker upstream, and a gG-250 A fuse downstream (calculation performed by the Ecodial software).

I²t OFF	I²t ON

Activate the I²t function (I²t ON) on the short-time protection to provide coordination.