We have 10 energy meter in that 4x of them are giving the negative reading. The events shown are two 1005- Negative Power Element 2 Warnings & 1007 Negative Total Power Warning. The plant is not generating power & we are not sure where this export power coming from on site We have verified the voltage connection, CT reversal & alignment but all is fine. Supplied a new meter which shows the same readings. We have concluded the negative reading could be associated with the equipment connected. The “issues” with the meters are on DB boards where the board is connected to air handling units which are full of variable speed drives and I think that some of these may be DC drives. If that is the case, this may be causing the reverse power flow,??? What effect VSD’s will have on the meter readings?
What impact will VSDs have on meter readings ?
What is Variable Speed Drive (VSD)?
Variable Speed Drive is more often referred to as a variable frequency drive (VFD) or an adjustable speed drive (ASD). It is an instrument of machines that allows one to modify the input voltage & frequency of an electric motor in order to adjust the speed & torque of the motor.
What impact will VSDs have on meter readings ?
When a variable speed drive (VSD) is used to adjust the speed of a motor, the meter readings may be affected in a variety of ways, depending on the application and the particular set of conditions.
Some potential results include the following:
1). Energy Consumption
2). Efficiency of the Motor
3). Power Factor
4). Harmonics
1). Energy Consumption
When controlling the speed of a motor using a variable speed drive (VSD), users may frequently accomplish reductions in energy consumption.
When opposed to when it is operating at full speed constantly, a motor that is operated at a lower speed utilising a variable speed drive (VSD) uses less energy.
This may result in a lower overall energy consumption as well as perhaps lower meter readings, which would indicate decreased overall power use.
2). Efficiency of the Motor
Electric motors typically operate most effectively under a load that falls anywhere between 75 and 100 percent of their rated capacity.
When employing a variable speed drive (VSD), it is possible to enhance the efficiency of a motor by running it at a lower speed. This indicates that the motor is able to transfer a greater proportion of the electrical energy that it consumes into the beneficial mechanical work that it needs to carry out.
As a result of this, the readings on the meters may indicate that efficiency has increased and that energy consumption has decreased.
3). Power Factor
The power factor of a system is a measurement of how efficiently the system uses the electrical power that is supplied to it. A motor’s power factor may be affected by variable speed drives (VSDs).
The use of a VSD may, under certain conditions, enhance the power factor, resulting in a more effective utilisation of energy potentially influencing the readings on the meters.
4). Harmonics
It is possible for variable speed drives (VSDs) to feed harmonic currents into electrical system.
Currents (or) voltages with frequencies that are the multiples of the fundamental frequency (usually 50 Hz or 60 Hz) are referred to as harmonics. Harmonics may be found in electrical circuits.
These harmonics have the potential to disrupt the waveform of the electrical current, which causes additional strain on the system. Harmonics may cause larger energy losses & increased meter readings if they are not effectively controlled.
This is because reactive power consumption causes higher meter readings.
Summary
It is necessary to keep considering that the particular effect that VSDs will have on meter readings will be determined by a wide range of elements, such as the kind of motor, the load profile, the control strategy, and the overall design of the system.
Any possible increase in losses carried on by harmonics may be compensated in certain situations by the energy savings & efficiency improvements obtained by variable speed drives (VSDs).
It may be helpful to analyse the unique impact of variable speed drives (VSDs) on meter readings in a given application by consulting with electrical engineers (or) energy specialists.