MEASURING TRANSDUCERS
ACTIVE • REACTIVE POWER
MTR02-U series measuring transducers by EPESOL are the best solution for utility applications of active (Watt) and reactive (Var) power measurements for 3-phase balanced and unbalanced networks. With IEC-60688 compliance, MTR02 series transducers offer a wide range of D.C linear current outputs. MTR02 transducers are highly accurate, yet mechanically durable with proven field time, internationally.
Operation
The MTR02-U range of transducers are precision measurement utility grade active (P/Watt) and reactive (Q/Var) power transducers for 3-phase balanced or unbalanced power systems. The input measurands (inputs) being fed from CT and VT (or directly) are converted into load-independent linear DC milliamperes output. This way the true R.M.S active (P) or reactive (Q) power is measured. MTR02 range transducers are powered through an Auxiliary supply connected to terminals 1 (L/+) and 2 (N/–), Input measurands (current and voltage) are supplied to terminals 7 to 16 while the Output(s) are taken from terminals 3 and4 (if the no. of outputs ordered are two, then the second output is available from 5 and 6). Each MTR02 unit is factory calibrated for its input and range which is selectable through the “ Ordering Information”. MTR02 provides a linear output current which is selectable through the “ Ordering Information” in five ranges.
Principal circuit
– IEC 60688 compliant
– Surface and DIN rail mount
– Category III overvoltage inputs
– Degree of pollution 2
– Option to select from 5 linear current outputs
– High voltage impulse withstand
– High dielectric insulation
– Up to 125% input overload measurement capability
– Works with 3-phase 4 wire balanced or unbalanced networks
– Selectable accuracy class index from CI. 1 or CI. 05
– Excellent cost-performance balance
Applications
Analogue and Digital Measurement Systems
– PLC Systems
– SCADA Systems
Operation details
Transducers, essentially, are the transformation circuits that provide galvanic isolation for the data recording devices. Measurement power transducers extract the active or reactive component from the apparent power. The equivalent circuit of the transducer is shown in Fig-1. All analogue output power transducers have input circuit impedance Zin and independent output impedance Zout The input and outputs are galvanically isolated. Transducer acts as an ideal current source producing an output current I1 which is the linear function of the input active or reactive power (Pin or Qin). Zout is actual output impedance of I1 and is in parallel to it. Zout shunts a small fraction, I2 , of the output current. The actual output current, thus is, Iout , equal to (I1 –I2).
For MTR02-U series transducers, the measurment of power is done using the time domain multiplication of indiviual currents and voltages per phase and then summation of individual phase power. Multiple samples per cycle are extracted from the analouge inputs from CT and VT after filteration. The currents and voltages for each phase and ground is then coverted to R.M.S values before multiplication. The formulas over one time constant (T) are below:
Line Voltage (R.M.S.): Line Currents (R.M.S.):
The current from neutral is the sum of individual line currents.
Active Power:
intakes the current and voltage signals and provides proportional output. To correspond this output with the power there are two conventions:
Reactive Power:
Secondary scaling:
Fig-1
Analogue output signals
MTR02 outputs are current based only and are factory selectable based on MOQ. Details are available in " Technical Specification". MTR02 series cater for wide-range of transfer fucntions, including offset zero and bi-directional output. Usual output ranegs are 4...20 mA and -10...0...+10 mA.
Compliance voltage
The compliance voltage is the value of the voltage appearing across the output terminals. This is an accuracy limiting output voltage for variable output load transducers having a current output.
The compliance Voltage for MTR02 is 15 V at maximum output current.
Output Scaling
Fundamentally, transducers are scaling instruments that provide the galvanic isolation. However, the scaling of power transducer is convention specific. A power transducer only
Transducer output is related to the current and voltage inputs applied directly to the transducer inputs and the output of the transducer corresponds with the secondary values of instrument transformers. So, a secondary scaled 110V and 5A input and 20mA output transducer will give 20mA output at 110V and 5A input. Secondary scaling is desirable when the output power is not known and associated metering is scaleable.
Primary scaling:
Transducer output correspnds to the line voltages and currents at the maximum power including the effect of overloading. The maximum power corresponds to the maximum output of transducer. So, for a -300...0...+300MW power transducer with bi-directional output, say -10...0...+10mA, will give 10mA at 300MW input.
4-quandrant power operation
Using trignometric identities, the power is often computed as the vector S=P+jQ, where the reactive power (Q, in VAr units) is plotted on the ordinate axis, and real power (P, in Watts) is plotted on the abscissa. This represents the power flow on the Cartesian plane.
This signifies the supply of P and Q in Quadrant-I, consumption of P in Quadrant-II, consumption of P and Q
in Quadrant-III, and consumption of Q in Quadrant-IV.
Class index
MTR02 series transducers have the option for two class indexes; CI. 1 or CI. 0.5. As per IEC 60688, the limit of error in output is ±0.5 % of fiducial value for CI. 0.5 transducers and ±1 % of fiducial value for CI. 1 transducers providing the physical conditions do not vary.
If, a transducer is classified as CI. 1, for example, it does not mean that the error under practical conditions of use will be within ± 1 % of the actual value of the output. It means that the error should not exceed ± 1 % of the expected value under closely specified conditions. As per IEC 60688, if the influencing parameters, like auxiliary supply, temperature, etc. are varied between the specified limits, a variation may occur comparable with the value of the class index.
Residual ripple for outputs
As per IEC 60688, the maximum ripple content in the output signal shall not exceed twice the class index. For the Cl. 0.5, this 1 % and 2 % for the CI. 1
Over-range capability
MTR02-U series power transducers cater for 120 % of their input measurands.
As per IEC 60688, if there is such a case, the difference between the intrinsic error at 100 % and the error at 120 % (under reference conditions) of the nominal value of the input shall not exceed 50 % of the class index. So for CI. 1 transducers that is 1.5 % and for CI. 0.5 that is 1% above maximum output value. In a 0 to 20 mA output transducer, 20 mA is the maximum output value and 120% of it will be 24 mA. So between 20 mA to 24 mA output, the transducer of CI. 1 may have error of 1.5 % instead of linear 1 % of fiducial value.
Technical Specifications
Performance
Ordering Information
† Please specify VT ratio, CT ratio, and Measuring range. Example: MTR02-UP-D1 10