Page 272 - Industrial Power Engineering and Applications Handbook

Philosol 3hy of quality systems and testing of electrical machines 11/251
rule of thumb, a temperature rise of 10% more than The current transformers and voltage transformers, when
the rated may reduce the life ofthe insulation by 40- used, must conform to IEC 60044 and IEC 60 186, as
50%. See Section 9.2 for more details. noted in the list of standards. Instrument transformers
4. Torque characteristics, i.e. starting torque, pull-out with the following accuracies must be used:
torque and pull-in torque, in the entire speed range to
ensure that the motor will develop adequate torque at For routine tests: Class 1 accuracy
all speeds to meet the load requirement. See Section For type tests: Class 0.5 accuracy
1.5 for more details.

On an assembled motor the following visual checks Quality of test power suppZy
are performed before it is run:
VOltLlge
1 That all the covers and canopies are fitted in their The voltage must approach a sinusoidal waveform and
correct locations. should be balanced. If at the time of conducting the
2 Special-purpose motors such as increased safety tests the voltage is almost but not coinpletely balanced,
motors, flame-proof or explosion-proof motors must arithmetical average of the phase voltage must be used
be checked for gaps, clearances and creepage distances for calculating the machine's performance.
of all the mating parts forming flame paths. The
construction of these motors must follow IEC 60079 Note
as noted in the list of standards. I The voltage i\ considered to be virtually \inu\oidal if none of
3 The terminal box for its correct position the instantaneow values of the wave differ from the instantaneous
4 The terminal box for proper connections, number of value of the same phase of the fundamental wave by more than
terminals and their markings 5% of the amplitude of the latter (TEC 60033-1).
5 The correct direction of rotation of the cooling fans 2 A rystem of three-phase voltage is considered to he lirtually
6 The heaters and thermistors when provided balanced if none of the negative hequence components eyceeds
14 over long periods or 1.5% for short periods of a few minute?
7 The clearance and creepage distances between the and zero sequence components exceed I% of the positive
terminals and between each terminal and the ground. sequence components (IEC 60034-1 1. See also Section 12.2

On a wound rotor motor, the following additional checks Current
are also necessary after removing the slip-ring covers, The line current in each phase of the motor should be
prior to testing: measured. If the line current is not exactly equal in all
phases, the arithmetical average of the phase current
1 The numbers. size and grade ofthe brushes and whether must be used for calculating the machine's performance.
the brushes are bedded properly to the contours of the
slip-rings Power
2 Whether the brushes are free to move in the brush Power input to a three-phase machine may be measured
holder and are not slack by two single-phase wattmeters, connected as in the
3 The brush spring tension. Brush pressure, when two-wattmeter method. (Section 1 I .4.3). Alternatively
measured, using finger spp',ing balance, should be a single polyphase wattmeter may be used.
between 1 SO and 200 N/cm-.
4 Whether the brushes are set concentrically on the Frequency
slip-rings. and each individual brush holder is set
approximately 2-2.5 mm from the slip-ring surface. The frequency should be maintained ac close to thc
Slip-rings must be concentric and free from damage rated frequency as possible. Any departure from the
and blow holes. rated frequency will affect the iosses and the efficiency
as shown in Section 1.6.2.
After the above checks the motor can be subjected to
type and routine tests. For testing instruments, the 11.2.2 Type tests
following class and grades are recommended. Type tests are conducted on the first machine of each
type or design to determine the characteristics and
11.2.1 Electrical measurements demonstrate its compliance with the relevant Standards.
These tests provide a standard reference for any subsequent
Selection of testing instruments similar machine. The following are the type tests according
to lEC 60034-1:
The indicating instruments used for electrical measure-
ments must conform to IEC 6005 1 and have the following 1 Resistance measurement of all windings and auxiliary
accuracies: devices (heaters and thermistors. etc.), when the
machine is cold (at room temperature)
0 For routine tests: class 1 .O or better, and 2 (i) Temperature rise test at full load
For type tests: not inferior to class 0.5. (ii) Resistance measurement of all the windings and