Siemens SIPROTEC 7SJ62 Manual page 172

Multi-functional protective relay with local control

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2.8 Motor Protection

Example: Motor with the following data:

Rated Voltage

Nominal current

Startup current

Startup duration

Permitted starts with cold motor

Permitted starts with warm motor

Current transformer

The following settings are derived from these data:

The following settings are made:

IStart/IMOTnom = 4.9

I MOTOR NOMINAL = 0.6 A

T START MAX = 8.5 s

MAX.WARM STARTS = 2

#COLD-#WARM = 1

For the rotor temperature equilibrium time, (address 4304) a setting time of approx. T Equal = 1 min has

proven to be a good value. The value for the minimum inhibit time T MIN. INHIBIT depends on the motor

manufacturer, or by the user's requirements. It must in any case be higher than 4304 T Equal. In this example,

a value has been chosen that reflects the thermal replica (T MIN. INHIBIT = 6.0 min).

The motor manufacturer's, or the requirements also determine also the extension factor for the time constant

during cool-down, especially with the motor stopped. Where no other specifications are made, the following

settings are recommended: Kτ at STOP = 5 and Kτ at RUNNING = 2.

For a proper functioning, it is also important that the CT values and the current threshold for distinction between

stopped and running motor (address 212 BkrClosed I MIN, recommended setting ≈ 0.1 I

set correctly. An overview of parameters and their default settings is generally given in the setting tables.

C53000-G1140-C207-2, Release date 01.2008

SIPROTEC, 7SJ62/64, Manual