TROUBLE SHOOTING FOR H.V. MOTORS

Temperature

The temperatures rise at various parts of the motor due to the heat loss dissipated in the motor. An excessive temperature rise will cause the deterioration of the insulation, and so the temperatures of the coils and adjacent core are to be kept below the specified temperature rise limit. There are the following three different methods for temperature measurement.

Thermometer Method

This is a method of measuring temperatures by fitting thermometers to the measuring parts of a motor. Usually, thermometers are fitted to the frame or to the bearings. This method is widely used for temperature measurement.

Resistance Method

This is a method of measuring the mean temperature of the coil by utilizing the change of the coil resistance with the temperature; the temperature is calculated in the following way.

where, 

R₂ : Coil resistance in heated condition (temperature t₂)

R₁ : Coil resistance in cold state (temperature t₁)

t₂ : Coil temperature immediately after test (ºC)

t₁ : Temperature obtained at the time of measuring R1in cold state

t₀ : Reference ambient temperature at the last of the test (ºC)

t : Temperature rise of coil (ºC)

T : Constant                T = 234.5 for copper

 T = 230.0 for aluminum

T = ……….A1

Embedded Resistance Temperature Detector (RTD) Method

This is a method of measuring temperatures of winding and bearings by means of RTDs embedded. (Only applied to the 6.9 KV motors.) The temperature settings for alarm and trip are recommended as follows:

Motors	Motor parts		Expected Temperature	Temp. Limit of Windings and Bearings	Settings
					Alarm	Trip
2620 KW (vertical)  18 poles  Seawater  Supply  Pump Motors	Windings		145	150	160	170
	Bearings	Upper Guide	75	90	90	100
		Thrust	70	90	90	100
		Lower Guide	75	90	90	100
1420 131(vertical)  10 poles  Brine Recycle  Pump Motors	Windings		140	150	160	170
	Bearings	Upper Guide	75	90	90	100
		Thrust	75	90	90	100
		Lower Guide	85	90	90	100
570KW(horizontal)  8 poles Product Water Booster  Pump Motors	Windings		120	150	1160	170
	Bearings	Front	65	95	95	105
		Rear	65	95	95	105

Table 1-1 Recommended Temperature Setting

TROUBLE SHOOTING FOR H.V. MOTORS part 2