Long-Time Protection

Presentation

Long-time protection on MicroLogic 6 E-M trip units protects all types of motor applications against overload currents.

Operating Principle

Long-time protection is I²t IDMT (Inverse Definite Minimum Time):

It incorporates the motor thermal image function.
It can be configured as the Ir pickup and as the trip class Class.

Tripping curve:

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The long-time protection parameters are:

A: In Trip-unit setting range
B: Ir Long-time protection pickup
C: Cl Long-time protection trip class (according to standard IEC/EN 60947-4-1)

NOTE: The SDTAM module early tripping protection function can be used to command contactor opening.

Setting the Long-Time Protection

Set the Ir pickup:

With the MicroLogic trip unit Ir 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 trip class Cl:

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)

Ir Pickup Setting Value

The default Ir pickup setting value is In (maximum dial value).

The overload or thermal protection tripping range is 1.05–1.20 x Ir according to standard IEC/EN 60947-2.

The Ir pickup is preset by a dial.

In Rating	Preset values of Ir (A) depending on the trip unit In rating and the dial position
25 A	12	14	16	18	20	22	23	24	25
50 A	25	30	32	36	40	42	46	47	50
80 A	35	42	47	52	57	60	63	72	80
150 A	70	80	90	100	110	120	133	140	150
220 A	100	120	140	155	170	185	200	210	220
320 A	160	180	200	220	240	260	280	300	320
500 A	250	280	320	360	380	400	440	470	500

The accuracy range is + 5%/+ 20%.

Use the keypad to fine-tune the setting, in increments of 1 A:

The setting range maximum is the preset value displayed by the dial.
The setting range minimum is the minimum preset value.

Example:

A MicroLogic 6 E-M trip unit In = 500 A is preset by the dial at 470 A. The fine-tuning range on the keypad is 250–470 A.

Trip Class Setting Value

The class is set via the keypad, using any of the four defined values: 5, 10, 20, and 30.

The trip class corresponds to the value of the trip time delay for a current of 7.2 x Ir according to standard IEC/EN 60947-4-1.

The factory class setting value is 5 (minimum value).

The following table shows the value of the trip time delay depending on the current in the load for all four trip classes.

Current in the load	Trip class Cl
	5	10	20	30
	tr Trip time delay (s)
1.5 x Ir	120	240	400	720
6 x Ir	6.5	13.5	26	38
7.2 x Ir	5	10	20	30

Motor Thermal Image

The model representing heat rise and cooling in a motor load is identical to that used for the conductors. It is constructed according to the algorithm for calculating the thermal demand but this model takes account of the iron and copper losses.

The following figure represents the limit curves for the iron and copper components calculated by the MicroLogic 6 E-M trip unit (for class 20):

A Limit temperature curve for copper

B Limit temperature curve for iron

C Tripping curve (low envelope)

Thermal Memory

MicroLogic 6 E-M trip units incorporate a thermal memory which ensures that the conductors are cooled even after tripping: cooling lasts for 20 minutes before or after tripping.

Cooling Fan

By default, the motor thermal image is calculated taking account of the fact that the motor is self-cooled (fan mounted on the shaft end).

If the motor is force-cooled (forced ventilation), the calculation of the thermal image takes account of the shortest time constants for the cooling calculation.

The cooling ventilation parameters (Auto or Moto position) are set on the MicroLogic trip unit keypad or using EcoStruxure Power Commission software.