What can cause unbalanced phase voltages to a motor?
Unbalanced voltages usually occur because of variations in the load. When the load on one or more of the phases is different than the other(s), unbalanced voltages will appear. This can be due to different impedances, or type and value of loading on each phase.
What are some possible causes of unbalanced voltage?
Voltage unbalance is primarily due to unequal loads on distribution lines or within a facility. In other words, the negative or zero sequence voltages in a power system typically result from unbalanced loads causing negative or zero sequence currents to flow.
What is a current imbalance?
Current Unbalance. Page 1. Current Unbalance. For a three-phase supply, current unbalance is defined as the maximum deviation of any current phase from the average current, divided by the average current, often expressed as a percentage.
How much current unbalance is acceptable?
NEMA Standard MG 1 prescribes a 1% limit for voltage unbalance, noting that current unbalance can be expected to be six to 10 times the voltage unbalance on a percent basis. If the current unbalance exceeds 10%, the supply voltages should be corrected to less than 1% unbalance, or the motor must be de-rated.
What causes high amperage in motor?
Electrical overload or over-current is caused by an excessive current flow within the motor windings, exceeding the design current which the motor is able to carry efficiently and safely. This can be caused by a low supply voltage, resulting in the motor drawing in more current in an attempt to maintain its torque.
How can voltage imbalance be avoided?
Regularly monitor voltages at the motor terminals to verify that voltage unbalance is maintained below 1 percent. Check electrical system single-line diagrams to verify that single-phase loads are uniformly distributed. Install ground fault indicators as required and perform annual thermographic inspections.
What happens if load is unbalanced?
An unbalanced load occurs when there is significantly more power drawn on one side of the panel than the other. This can lead to overheating of electrical components and possibly overloading the panel.
What is voltage unbalance in motor?
Voltage unbalance occurs when the RMS line voltages on a poly-phase system are unequal. Voltages are seldom perfectly balanced between phases, but when this unbalance becomes excessive, it can create problems for poly-phase motors.
What causes the current through an electrical circuit to decrease?
The current in a circuit is directly proportional to the electric potential difference impressed across the circuit and inversely proportional to the resistance of the circuit. Reducing the current can be done by reducing the voltage (choice A) or by increasing the resistance (choice D).
What is the maximum current unbalance of a 3 phase motor?
Voltage unbalance exceeding more than 2 percent in three-phase systems can cause current unbalance among the windings. These, in turn, can cause an increase in winding temperature and an overheating problem that can be harmful to the motor.