Siemens MCC-3298 사용자 설명서

3 Operating the SAMMS-LV Device

3.19 Stator Protection

By selecting the overload class slightly greater than or equal to

the motors starting time, the motor model defines an energy I

value. In this value, I equals 600% of the motors full load current

and t equals the overload class selected.

If the amount of energy exerted by the motor during start, stall

or under locked rotor condition exceeds the amount of energy

defined by the overload class selected, the SAMMS-LV device

will trip. This protects the motors winding against excessive

heat build up. For example, a typical motor starts within 3 to 4

seconds. By selecting an overload class 4 or 5, you can safely

start the motor hot or cold and without nuisance tripping. This

also provides protection against stall time exceeding 4 or 5

seconds; assuming the locked rotor current equals 600% of the

motors full-load current (See Figure 3.10).

3.20 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 SAMMS-LV is not in start inhibit (See Section 3.21).

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 3.11 shows

a multi-start scenario for an open drip-proof motor.

Figure 3.11 Multi-start scenario for an open drip-proof motor

3.21 Start Inhibit

When the motor temperature reaches the maximum values

allowed, the SAMMS-LV 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.

3.22 Cooling Time Constants

The motor time constants vary based on whether the motor is

running idle or is stopped. The values listed in Table 3.4 are used

in the motor model.

Motor

Cond.

Delta

Temp.

Motor FLC

0.3-9.0A 9.1-65A

65.1-540A

Stopped 80º C to

29º C

1750 s

5500 s

9100 s

Running

Idle

80º C to

39.4º C

600 s

1800 s

2800 s

Table 3.4 Motor time constants

3.23 Normalized Temperature Rise for Class

B and Class F Insulation

Steady state and maximum winding temperature are functions

of the motors 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

Parameters

Class B

Insulation

Class F

Insulation

% Full Load

Temperature

Rise

Steady State

Temperature

rise at

full-load

current

80º C

105º C

100

Maximum

allowed

winding

temperature

140º C

185º C

175

Table 3.5 Steady state and maximum winding temperature rise

3.24 Ground Fault Detection

In SAMMS-LV 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),