Siemens SAMMS-MV Repetitive Starts, Start Inhibit, Cooling Time Constants, Ground Fault Detection

3 Operating the SAMMS-MV Device

ture of the rotor and provides a signal to trip the motor off-line when it reaches a trip temperature value. The motor model takes into account the change of the rotor resistance during motor startup. Rotor resistance is a function of motor slip; therefore, it is highest at locked rotor and decreases as the motor speeds, and the slip decreases.

You can select motor cold stall time from 5 to 100 seconds in increments of 1 second. The selected time will adjust the rotor loop elements so that the maximum temperature limit in the rotor is reached under locked rotor conditions for the time selected. If cold stall time is not known, the rotor model will assume a cold stall time based on the type of motor used. The user is allowed to select an open drip proof (ODP) motor or a totally enclosed fan-cooled motor (TEFC) motor. The default value for the ODP motor is 10 seconds. The default value for the TEFC motor is 20 seconds.

3.21 Repetitive Starts

The motor model allows repetitive starts without nuisance tripping while protecting the motor against overload and stall conditions. Repetitive starts can occur as long as the following conditions are met:

1.The energy exerted by the motor during start does not exceed the energy defined by the overload class selected.

2.The motor winding temperature does not exceed the maxi- mum temperature allowed.

3.The rotor temperature does not exceed the maximum temperature allowed.

4.The SAMMS-MV is not in start inhibit (See Section 3.22).

For example, a motor starting from cold condition could have 4 or more typical starts of 5 seconds without nuisance tripping and without damaging the motor insulation. Figure 3.12 shows a multi-start scenario for an ODP motor.

3.22 Start Inhibit

When the motor temperature reaches the maximum values allowed, the SAMMS-MV device trips. If you attempt a restart, the overload LED flashes and the motor will not start until the motor winding and rotor temperatures cool down to the full load temperature. HHC function F25 displays the motor winding temperature as a percentage of the full-load temperature. HHC function F10 displays the time to enable restart in seconds.

3.23 Cooling Time Constants

The motor time constant is a function of the motor type. The values listed in Table 3.4 are used in the motor model.

Motor	Delta	Motor Type
Condition	Temperature
		TEFC	ODP
Stopped	80º C to	9900 s	6000 s
	29º C
Running Idle	80º C to	7200 s	4500 s
	39.4º C

Table 3.4 Motor time constants

TEFC motors include the following types of motors:

∙Totally Enclosed Fan Cooled

∙Totally Enclosed Fan Cooled Explosion Proof

∙Totally Enclosed Air-to-Air Cooled (TEAAC)

ODP motors include the following types of motors:

∙Drip Proof Weather Protected I (WP-1)

∙Weather Protected II (WP-2)

∙Open Drip Proof

∙Totally Enclosed Water-to-Air Cooled (TEWAC)

3.24Normalized Temperature Rise for Class B and Class F Insulation

Steady state and maximum winding temperature are functions of the motor’s insulation class. In this motor model, normalized temperature rise for both Class B and Class F insulation are used. The motor winding temperature is displayed as a per- centage of the steady-state full-load temperature rise as shown in Table 3.5.

Boundary	Class B	Class F	% Full Load
Parameters	Insulation	Insulation	Temperature
			Rise
Steady State	80º C	105º C	100
Temperature
rise at
full-load
current
Maximum	140º C	185º C	175
allowed
winding
temperature

Table 3.5 Steady state and maximum winding temperature rise

3.25 Ground Fault Detection

In SAMMS-MV devices, HHC function F12 selects ground fault protection or warning.

∙protection = ON

∙warning = OFF

The device detects a ground fault if the fault current exceeds the pickup level for 360 msec. If you have selected protection (ON), the motor trips and the Ground Fault LED illuminates until reset. If you selected warning (OFF), the Ground Fault LED flashes as long as the fault current exceeds the pickup level. Table 3.6 lists the pickup levels for each overload size. Ground fault protection is locked out for 1.4 seconds following a start.

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