How to measure current and voltage?-Ammeter and Voltmeter for measurement

Today we are going to learn about the measurement of electrical parameters and their importance. 

Even though electrical energy is dangerous it is necessary to power up a load. This electrical energy can be generated at a generating station that is far away from the load, so it is very much important to control it from its origin point.  AC circuits and networks are helping very much to deliver this electrical energy to the load. Analyzation of power flow helps us to understand and control it.

How does the measurement process help in power analyzation?

Measuring electrical quantities help us to compare the power flow from normal to abnormal. If power flow is abnormal, we can easily identify it and can reduce the risk of danger.

What is used to measure electric current in a circuit?

Metering devices helps to measure electrical parameters such as current, voltage, frequency, power factor. 

  1. We measure the flow of electric current in amps and ampere (A) using the device ammeter.
  2. We measure the flow of electric voltage in volts (V) using the device voltmeter.
  3. We measure the flow of frequency in Hertz (Hz) using a frequency meter.
  4. We measure the power factor in PF using a power factor meter.
In simple words, the measurement process gives the real-time measurement data of power flow. If the measurement is abnormal we can conclude that the power flow is abnormal.

Measurement of voltage using voltmeter

We use a voltmeter to measure the flow of voltage in the circuit.

A voltmeter is a metering device connected across (parallel) the two points of the live conductor to measure the flow of voltage. (Voltmeter should be connected parallel to the load or winding). Unit of measurement of voltage is volts and symbolized by letter V or U.

CONNECTION  OF VOLTMETER

For measuring high voltage the voltmeter is connected to the secondary circuit of the voltage transformer. 

What is the function of VT in the measurement?

 For measuring high voltage in a live conductor, a voltage transformer is much necessary to step down the voltage from high to the rated voltage.

In a voltage transformer, the output voltage is directly proportional to the input voltage. Input voltage is nothing but the voltage which to be measured.

For instance, consider you have to measure the voltage of the 11Kv busbar using the voltmeter rated up to 440v (capacity of voltmeter). At this time you need to connect an 11 Kv / 440v rated voltage transformer to step down the busbar voltage to 400 v. Suppose the voltage transformer is supplying 440v in its secondary circuit (output) and the meter is showing 440v then we can conclude that the flow of rated busbar voltage is normal. If the secondary circuit is supplying 150v and the meter is showing 150v then we can conclude that the primary voltage is 3.75Kv which is busbar voltage.

Measurement of current using ammeter

We use an ammeter to measure the flow of current in the circuit.

An ammeter is a metering device connected series to the live conductor to measure the flow of current. (Ammeter should be connected parallel to the load or winding). Unit of measurement of current in Amps and symbolized by letter A.

For measuring high current the ammeter is connected series to the secondary circuit of the current transformer. 

What is the function of CT in the measurement?

 For measuring high current in a live conductor, a current transformer is much necessary to step down the voltage from high to the rated voltage.

In a current transformer, the output current is directly proportional to the input current. The input current for ct is nothing but the current which to be measured.

For instance, consider you have to measure the current of the 11Kv busbar (110A) using the ammeter rated up to 5 A (capacity of ammeter). At this time you need to connect the rated current transformer to step down the busbar current 110 to 5A. Suppose the current transformer is supplying 5A in its secondary circuit (output) and the meter is showing 5A then we can conclude that the flow of rated busbar current is normal that is busbar current. If the secondary circuit of the ammeter is supplying 2A and the meter is also showing 2A then we can conclude that the flow of busbar current is only 50A.


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