Chapter 3

A motor-feeder must satisfy the general rules of NEC standards as per Article 430. This standard defines:

• Disconnection from power supply

• Short-circuit protection

• Overload protection

• Motor control or switching

TeSys GV5PB / GV6PB devices:

• Provide protection for direct-on-line motor-feeders and star-delta motor starters (direct-on-line starting is the most widely used type of motor-feeder).

• Integrate the basic protections (overload, short-circuit, and phase unbalance) for the motor-feeder.

• Allow protection and coordination of the motor-feeder components that comply with the requirements of UL 489 Supplement SH.

• Are used to create motor-feeders with two devices.

TeSys GV5PB / GV6PB devices consider the application to be operating as soon as the 10% of Ir pickup is crossed in a positive direction by the motor current.

Two operating states are considered:

• Startup state

• Steady state

The application is considered to be in startup state according to the following criteria:

• Start: As soon as the 10% of Ir pickup is crossed in a positive direction by the motor current.

• End: As soon as the Id pickup equals 1.5 x Ir and the td time delay equals 10 s (non-adjustable parameters).

Exceeding the 10 s time delay does not result in tripping.

NOTE: The trip unit filters the subtransient state (first current peak of approximately 20 ms on contactor closing). This current peak is not therefore taken into account when assessing whether the Id pickup has been crossed.

The application is considered to be in steady state according to the following criteria:

• Start: As soon as startup ends.

• End: As soon as the 10% of Ir pickup is crossed in a negative direction by the motor current.

The following diagrams show the two cases of transition between startup and steady state:

Operating states with current I < Id before end of td	Operating states with current I > Id at end of td

The trip unit is suitable for protecting motor-feeders in standard applications. The thermal trip curves are calculated for self-ventilated motors. The adjustment dials and indications are located on the front face.

TeSys GV5PB trip unit

TeSys GV6PB trip unit

Indication LEDs on the front of the trip unit indicate its operational state.

The indication LEDs function for device load currents above 30 A.

The following figure and table define the protection functions performed by the trip unit:

Each function is reviewed in detail on the following pages.

Set the overload or thermal protection pickup (Ir), the short-time protection pickup (Isd), and trip class (Class) by using the dials on the device.

The GV6PB motor protection circuit breaker supports reflex tripping. The system of reflex protection breaks very high fault currents by mechanically tripping the device with a piston actuated directly by the pressure produced in the device from a short-circuit. This piston operates the opening mechanism, resulting in ultra-fast device tripping.

Overload or thermal protection protects all types of motor applications against overload currents.

GV5PB
	The long-time protection is set by two dials according to the starting characteristics of the application. The pickup setting Ir for trip unit long-time protection is expressed in amperes:
GV6PB
	This value corresponds to the operating current used in the motor application. The maximum Ir setting corresponds to the trip unit rating In.

Overload or thermal 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:

The overload or thermal protection pickup (Ir) is set by using a multi-position dial.

The default Ir pickup setting value is 0.4 x In (minimum dial value).

The overload or thermal protection tripping range is 1.05 ˗ C1.20 x Ir according to IEC/EN 60947-4-1 standard.

The following table shows the preset values of the adjustment dial Ir in amperes for each current rating In:

The trip class (Class) is set by using an adjustment dial:

• Class 5

• Class 10 (default value)

• Class 20

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

The model representing heat rise and cooling in a motor load is constructed according to the algorithm for calculating the thermal demand, taking account of the iron and copper losses.

The following figure represents the limit curves for the iron and copper components calculated for class 20:

The trip unit uses a thermal memory function to protect the motor from overheating in case of repetitive low amplitude overload conditions.

Electronic protection without thermal memory function does not protect against repetitive low amplitude overload conditions because the duration of each overload above the pickup setting is too short to cause tripping. However, each overload causes a temperature rise in the installation. The cumulative effect of successive overloads can overheat the system. The thermal memory function remembers and integrates the thermal heating caused by each pickup setting overrun. The thermal memory function remembers the thermal heating values for 20 minutes before or after tripping.

Example: Comparison of the heat rise calculation without thermal image (diagram A) and with thermal image (diagram B):

Diagram A	Diagram B

With thermal image, the trip unit adds the thermal effect of successive current pulses. Tripping occurs based on the actual thermal state of the motor.

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

Short-time protection protects all types of motor applications against short-circuit currents.

Short-time protection lets through motor starting currents but protects cables and motor starter devices and allows not to oversize them (useful for wide range settings devices).

Short-time protection is definite time. It can be configured as the Isd pickup.

Tripping curve:

The short-time protection pickup Isd is set by using a multi-position dial. The setting value is expressed in multiples of Ir.

The precision range is +/-15%.

The time delay cannot be adjusted.

• The hold time is 20 ms.

• The maximum breaking time is 60 ms.

Instantaneous protection is fixed: the pickup value is determined by the current rating In. Protection is instantaneous.

Instantaneous protection is fixed: the pickup value is determined by the current rating In. Protection is instantaneous.

Tripping curve:

The Ii pickup value is 15 x In (trip unit rating In corresponds to the maximum Ir setting).

The precision range is +/-15%.

The maximum breaking time is 30 ms.

Phase unbalance protection:

• Calculates the current unbalance for each phase, compared to the average current, expressed as a percentage:

• Compares the value of the maximum current unbalance with the Iunbal protection pickup.

The following diagram shows a maximum positive unbalance on phase 2:

If the maximum current unbalance value is higher than the phase unbalance protection Iunbal pickup, the tunbal time delay is actuated.

Phase unbalance protection cannot be deactivated.

Phase unbalance protection is activated during startup and in steady state.

The phase unbalance (or phase loss) protection trips if the current unbalance exceeds the 30% fixed pickup Iunbal during a fixed tunbal time delay. The tunbal time delay differs according to the motor operating conditions:

• Start-up phase: tunbal = 0.7 s

• Steady state phase: tunbal = 4 s

		A	Activation of startup phase.
		B	Activation of protection time delay as soon as the pickup is crossed.
		C	Protection tripped at the end of the fixed time delay of 0.7 s
		1M	Motor current
		1D	Maximum unbalance of the motor phase currents
		2A	Monitoring by phase unbalance protection during startup
		White: Not active
		Green: Active

		In steady state:
		A	Activation of steady state phase.
		B	Activation of protection time delay as soon as the pickup is crossed.
		C	Protection tripped at the end of the fixed time delay of 4 s.
		1M	Motor current
		1D	Maximum unbalance of the motor phase currents
		2B	Monitoring by phase unbalance protection in steady state
		White: Not active
		Green: Active

The phase unbalance protection does not trip if the current unbalance falls below the Iunbal pickup before the end of the fixed tunbal time delay.

		A	Activation of steady state phase.
		B	Activation of protection time delay as soon as the pickup is crossed.
		C	Time delay is reset.
		1M	Motor current
		1D	Maximum unbalance of the motor phase currents
		2B	Monitoring by phase unbalance protection in steady state
		White: Not active
		Green: Active