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# Problems

Author: E.E. Kimberly

 Problem Answer 1 A millivoltmeter with a range of 0 to 50 is to be used with a 400-amp, 50-millivolt shunt. What will be the constant for this combination? 2 What is the resistance of a 50-millivolt shunt rated at 10 amp? 3 A direct-reading 5-amp, 100-volt wattmeter is used with a potential transformer of 20:1 ratio and a current transformer of ,50:5 ratio. By what constant must the reading be multiplied? 4 Give complete instructions for proving the correctness of connections of a polyphase wattmeter, using both current and potential transformers, when measuring a balanced three-phase three-wire load. 5 A 50-millivolt meter draws 1 milliampere for every 5 millivolts impressed on it. How many ohms in series must be added to cause the meter to read full scale on 150 volts? 6 A voltmeter with a resistance of 15,000 ohms draws 10 milliamperes with full scale deflection. How could this meter be converted to a satisfactory milliammeter with 10 milliamperes full scale? 7 It is required to measure a d-c voltage of about 700 volts. A 600-volt meter and a 150-volt meter are available. Is it permissible to use these meters in series and to add their readings? Explain. 8 In using an ammeter and a wattmeter in the secondary circuit of a current transformer, why must the current coils be connected in series? 9 In using a voltmeter and a wattmeter in the secondary circuit of a potential transformer, why must the potential coils be connected in parallel?

Last Update: 2011-01-18