Wednesday, February 24, 2010

Electrical Interview questions Part 16

Query:What is the function of interposing current transformer? 
Resolution:The main function of an interposing current transformer is to balance the currents supplied to the relay where there would otherwise be an imbalance due to the ratios of the main current transformers.  Interposing current transformer are equipped with a wide range of taps that can be selected by the user to achieve the balance required. 

Query:What are Motor Generator Sets and explain the different ways the motor generator set can be used ? 
Resolution:Motor Generator Sets are a combination of an electrical generator and an engine mounted together to form a single piece of equipment. Motor generator set is also referred to as a genset, or more commonly, a generatorThe motor generator set can used in the following different ways: 
              1.Alternating current (AC) to direct current (DC)
              2.DC to AC
              3.DC at one voltage to DC at another voltage
              4.AC at one frequency to AC at another harmonically-related frequency

Query:What is power quality meter ?

Resolution:Power Quality meters are common in many industrial environment. Small units are now available for home use as well. They give operators the ability to monitor the both perturbations on the power supply, as well as power used within a building, or by a single machine or appliance. In some situations, equipment function and operation is monitored and controlled from a remote location where communication is via modem, or high-speed communication lines.So we can understand the importance of power measurement through power quality meters.

Query:What is the different between digital phase converter and ordinary phase converter?
Resolution:Digital phase converter are a recent development in phase converter technology that utilizes proprietary software in a powerful microprocessor to control solid state power switching components. This microprocessor, called a digital signal processor (DSP), monitors the phase conversion process, continually adjusting the input and output modules of the converter to maintain perfectly balanced three-phase power under all load conditions.

Query:Explain the operation of variable frequency transformer?
Resolution:A variable frequency transformer is used to transmit electricity between two asynchronous alternating current domains. A variable frequency transformer is a doubly-fed electric machine resembling a vertical shaft hydroelectric generator with a three-phase wound rotor, connected by slip rings to one external ac power circuit. A direct-current torque motor is mounted on the same shaft. Changing the direction of torque applied to the shaft changes the direction of power flow; with no applied torque, the shaft rotates due to the difference in frequency between the networks connected to the rotor and stator.The variable frequency transformer behaves as a continuously adjustable phase-shifting transformer. It allows control of the power flow between two networks .

Query:What is the main use of rotary phase converter ?
Resolution:Rotary phase converter will be converting single phase power into true balanced 3 phase power,so it is often called as single phase to three phase converter .Often the advantages of 3 phase motors, and other 3 phase equipment, make it worthwhile to convert single phase to 3 phase so that small and large consumers need not want to pay for the extra cost of a 3 phase service but may still wish to use 3 phase equipment.