How is the 90-degree phase shift achieved in a Var transducer?

  • Thread starter Thread starter kanishke007
  • Start date Start date
  • Tags Tags
    Watt
AI Thread Summary
A Var transducer achieves a 90-degree phase shift necessary for calculating reactive power (Vars) by modifying the physical arrangement of its windings, similar to a Watt transducer. This phase shift is essential for converting real power measurements into reactive power by utilizing the sine of the phase angle. Historically, electromechanical meters used eddy-current motors with specific winding configurations to produce the required torque proportional to the electric fields. Modern devices have transitioned to microprocessors and digital signal processing for improved accuracy, although older mechanical meters were often more reliable in non-linear load scenarios. The discussion highlights the evolution of metering technology and the continued relevance of older methods in certain applications.
kanishke007
Messages
2
Reaction score
0
A Watt transducer has line to line voltages and line currents as inputs. It calculates the Watts and outputs DC mA. The one i am working on is rated 1mA DC for 500W AC. The relationship is linear.

A Var transducer does exactly the same, but it shifts the input AC by 90degrees to get Vars.

My question is: How do we mechanically/electrically achieve the 90deg ph. shft. in the construction of the Var transducer ?
 
Engineering news on Phys.org
Volt-ampere reactive (var) is calculated by multiplying the rms values of the potential (volts), current (amps), and the sine of the phase angle between them.

http://en.wikipedia.org/wiki/Volt-amperes_reactive"
 
Last edited by a moderator:
You are absolutely right. However, that was not my question.

The Var transducer is the same physical device as the Watt transducer. However, to make the Watt tranducer output Vars, there is a phase shift of 90degs applied to the real power hence making it cos(90-angle)=sin(angle), which gives us Vars. So, my question is, how is this phase shift applied mechanically ? is it something to do with the way the turns are wound on the coil ? or something else perhaps ?

thanks
 
Well, the transducer measures the phase angle and makes the calculation.

Check out Figure 3 (Application diagram for phase to phase reverse VAR connection) for their Type MWTU 11 Forward and Reverse Power Relay.

"www.electricalmanuals.net/files/RELAYS/ALSTOM/MWTU/R8127B.pdf"[/URL]

Here they use a phase sensitive bridge.
 
Last edited by a moderator:
Long ago, electricity power meters (kWh, kVAh and kVArh) operated using eddy-current motors that spun a metal disk. The disk was connected via gears to a series of mechanical dials which could be visually read. The various windings for the eddy-current motors were wound such that the mechanical arrangement produced torque in the disk proportional to the product of the electric fields from the current-windings and the voltage-windings. The phase relationship was alterable during the construction via the relative physical relationship between the windings.

The days it is all done with microprocessor devices & digital signal processing methods. For the most part, this is an improvement, as the old electromechanical instruments would develop inaccuracies as the jewel bearings became worn. However, the older meters were actually more accurate in measuring power in non-linear loads.
 
Hi MThornton,

I bet they are still used a lot. In the '80s when I was involved with watt/var metering, these mechanical meters were used in tie-line substations (metering between two areas/companies) to account for MegaWattHours being sold and bought. The disk had a pattern of holes that allowed light to be detected, creating pulses; each representing 1 MWH.
 
I used to be an HVAC technician. One time I had a service call in which there was no power to the thermostat. The thermostat did not have power because the fuse in the air handler was blown. The fuse in the air handler was blown because there was a low voltage short. The rubber coating on one of the thermostat wires was chewed off by a rodent. The exposed metal in the thermostat wire was touching the metal cabinet of the air handler. This was a low voltage short. This low voltage...
Hey guys. I have a question related to electricity and alternating current. Say an alien fictional society developed electricity, and settled on a standard like 73V AC current at 46 Hz. How would appliances be designed, and what impact would the lower frequency and voltage have on transformers, wiring, TVs, computers, LEDs, motors, and heating, assuming the laws of physics and technology are the same as on Earth?
Thread 'How Does Jaguar's 1980s V12 Dual Coil Ignition System Enhance Spark Strength?'
I have come across a dual coil ignition system as used by Jaguar on their V12 in the 1980's. It uses two ignition coils with their primary windings wired in parallel. The primary coil has its secondary winding wired to the distributor and then to the spark plugs as is standard practice. However, the auxiliary coil has it secondary winding output sealed off. The purpose of the system was to provide a stronger spark to the plugs, always a difficult task with the very short dwell time of a...
Back
Top