Three-phase four-wire transformer reactive power meter miswire analysis - News

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In the electric energy metering, the wrong wiring of the transformer will cause the measurement of the active energy to be inaccurate. In fact, the wrong wiring of the transformer will also affect the measurement of the reactive energy, which makes the measurement of the user inaccurate. Here are a few examples of the impact of the wrong wiring of the transformer on the measurement of reactive energy.
1 The three-phase current transformer secondary polarity full connection inverse power expression is: Qa = IaUbccos (90 Â° + Ï†a)
Qb=IbUcacos(90Â°+Ï†b)
Qc=IcUabcos(90Â°+Ï†c)
The power of the three components is: Q = Qa + Qb + Qc
=IaUbccos(90Â°+Ï†a)+IbUcacos(90Â°+Ï†b)+IcUabcos(90Â°+Ï†c)
=-(IaUbcsinÏ†a+IbUcasinÏ†b+IcUabsinÏ†c)
When the three-phase circuit is balanced, Ua=Ub=Uc
Ia=Ib=Ic
Î¦a=Ï†b=Ï†c
Then Q=-3IaUbcsinÏ†a
Actual reactive power Q'=3IaUbcsinÏ†a
Therefore, the reactive energy meter is reversed, and the counter-measurement value of the reactive energy meter is substantially equal to the normal measured value.
2 Two-phase voltage components are connected incorrectly. A. C two-phase voltage components are connected incorrectly, and the power expressions of each component are:
Qa=IaUbacos(150Â°-Ï†a)
Qb=IbUaccos(90Â°+Ï†b)
Qc=IcUcbcos(30Â°-Ï†c)
When the three-phase circuit is balanced, the sum of the three component powers is:
Q=Qa+Qb+Qc electrician's home=IaUbacos(150Â°-Ï†a)+IbUaccos(90Â°+Ï†b)+IcUcbcos(30Â°-Ï†c)
=IaUba(cos150Â°Ã—cosÏ†a+sin150Â°Ã—sinÏ†a-sinÏ†b+cos30Â°Ã—cosÏ†c+sin30Â°Ã—sinÏ†c)=0
Therefore, when the two-phase voltage component is connected incorrectly, the reactive power meter does not rotate.
3 Two-phase current components are connected incorrectly. A and B two-phase current components are connected incorrectly, and the metering power expression of each component is:
Qa=IbUbccos(30Â°+Ï†a)
Qb=IaUcacos(150Â°+Ï†b)
Qc=IcUabcos(90Â°-Ï†c)
When the three-phase circuit is balanced, the sum of the three component powers is:
Q=Qa+Qb+Qc
=IbUbccos(30Â°+Ï†a)+IaUcacos(150Â°+Ï†b)+IcUabcos(90Â°-Ï†c)
=IcUbc(cos30Â°Ã—cosÏ†a-sin30Â°Ã—sinÏ†a+cos150Â°Ã—cosÏ†b-sin150Â°Ã—sinÏ†b+sinÏ†c)=0
When the two-phase current component is connected incorrectly, the reactive power meter does not turn.
4 Two-phase current component and voltage component are connected at the same time. Assuming that the two-phase current component and the voltage component are connected incorrectly at the same time, the metering power expression of each component is:
Qa=IcUbacos(90Â°+Ï†a)
Qb=IbUaccos(90Â°+Ï†b)
Qc=IaUcbcos(90Â°+Ï†c)
When the three-phase circuit is balanced, the sum of the powers of the components is:
Q=Qa+Qb+Qc
=IcUbacos(90Â°+Ï†a)+IbUaccos(90Â°+Ï†b)+IaUcbcos(90Â°+Ï†c)
=-3IcUbacosÏ†a
When the two-phase current element and the voltage element are connected at the same time, the reactive power meter reverses at the same speed as the normal speed.
5 three-phase voltage A, B, C are sequentially connected to B, C, A phase, then the metering power expression of each component is: electrician's house Qa = IaUcacos (150 Â° + Ï†a)
Qb=IbUabcos(150Â°+Ï†b)
Qc=IcUbccos(150Â°+Ï†c)
When the three-phase circuit is balanced, the sum of the powers of the components is:
Q=Qa+Qb+Qc
=IaUcacos(150Â°+Ï†a)+IbUabcos(150Â°+Ï†b)+IcUbccos(150Â°+Ï†c) Information from:
=3IaUcacos(150Â°+Ï†a)
The actual reactive power is Q'=3IaUcasinÏ†a.
Since cos(150Â°+Ï†a) is always in the second and third phase limits, the reactive power meter is reversed.
6 Three-phase voltage A, B, C are sequentially connected to C, A, B phase, then the metering power expression of each component is:
Qa=IaUabcos(30Â°+Ï†a)
Qb=IbUbccos(30Â°+Ï†b)
Qc=IcUcacos(30Â°+Ï†c)
When the three-phase circuit is balanced, the sum of the powers of the components is:
Q=Qa+Qb+Qc
=IaUabcos(30Â°+Ï†a)+IbUbccos(30Â°+Ï†b)+IcUabcos(30Â°+Ï†c)
=3IaUabcos(30Â°+Ï†a)
The actual reactive power Q' = 3IaUabsinÏ†a.
The analysis shows that when Ï†a>30Â°, the dynamometer is less metered.
When Ï†a <30Â°, the reactive meter is multimeter.
When Ï†a=60Â°, the dynamometer does not turn.
The variogram is inverted when Ï†a>60Â°.
7 Summary is just a simple analysis of several miswires of reactive power meters. In fact, there are many cases of miswired three-phase four-wire reactive power meters, but as long as we master the vector diagram analysis according to the above method, no matter what kind of misconnection We can generally analyze the measurement of the meter, so as to correctly calculate the user's reactive equivalent and avoid measurement misalignment.

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