Consequences of change of Voltage in AC Motors

Engines are operated at the voltage fluctuations mentioned. This does not mean that such an operation will comply with industry standards capacity, temperature increase, or, as a rule, the expected service life. Fig. 7-34 shows the General effects. Such effects are not guaranteed for specific engines.

Rising temperatures and operational characteristics of engines in a sealed hermetic compressor shells are a special case. These engines are cooled by suction gas return different numbers and temperature. Thus, Fig. 7-34 not necessarily applicable to this specialized type equipment.

The chart shows the approximate effect of change of voltage on the characteristics of the engine. The reference base voltage and frequency) is understood that shown on the nameplate of the мотор.

Some of the terms used in the graph are described here.

Normal slip = synchronous speed nameplate speed

Slip in the graph shows the change in normal slip. Synchronous speed 60 Hz motors

2-pole 3600 rpm or min
4-pole 1800 rpm or min
6-pole, 1200 rpm, or min
8-pole 900 rpm or min

Table 7-3 indicates the voltage drop, which may be provided for different amps flow through copper conductors of various gage size. Fig. 7-33 provides the same data in a graphical form.

These data are applicable to both single-phase and three-phase circuits. In each case the length of the wire is equal to twice the distance from the power distribution panel, devices, terminals, measured along the path of the conductors. That's twice the distance between B and C in Fig. 7-32, measured along the path of the conductors. For motorized equipment, in particular those that start under loaded conditions voltage terminals of the unit should not fall more than 10 percent below nameplate value, unless expressly approved by the manufacturer.

Thus, the voltage permissible load causes should expect any reduction below the nominal voltage, which can be caused at full load conditions at the point of connection of the power source (point A in Fig. 7-32).

Troublesome voltage loss can also occur elsewhere, if the electrical connections or connections mechanical imperfect and create unexpected resistance. Such compounds can exist in the distribution panel, the meter socket, or even where outdoor power drops pressed to the feeder lines on poles. Where there are large differences between no-load voltage and operating voltage, sources of voltage drop can be determined, taking readings of the voltmeter in different circuit. These points can be ahead of the meter, after the circuit breaker trip, the device terminals, and other locations.