Schneider Electric K series Instrukcja Użytkownika Pobierz pdf (Strona 39)

PLSED309039EN PM1000 Series Power Meters

08/2010 Chapter 5 – Installation

Auxiliary Supply (Control Power)

The PM1000 power meter requires a single-phase AC/DC auxiliary (control)

power supply to powerup its internal electronic circuitry. External surge

suppressors are necessary in the auxiliary supply circuit for proper operation

during extreme surge conditions, where the voltage surges exceed the

auxiliary supply limits (e.g.,rural areas and outlying areas prone to lightning

strikes).

Range:

 44 to 277 VAC/DC.

 Burden (load) < 3 VA at 240 V.

 The control power may be derived from the voltage signals.

 If you have a 440 V 3-wire delta system and a reliable neutral is not

available, use a 440 V: 240 V supply transformer to provide the standard

240 V auxiliary supply.

NOTE: It is much easier to set up the meter before you mount the meter on the panel. See

“Quick setup” on page 17 for more information.

PTs (VTs) and CTs

Large electrical installations have high voltages and currents, which may

exceed the direct connection rating of the power meter. In this case,

potential transformers (PTs) and current transformers (CTs) are used to

precisely step down or reduce the voltage and current levels to suit the

power meter rating. Potential transformers usually have a full scale output of

110 VAC RMS line-line and current transformers usually have a full scale

output of 5 A or sometimes 1 A.

The PTs (VTs) and CTs must be planned, installed, and tested by a qualified

electrical contractor before wiring the power meter. The accuracy of the

measurement also depends on the accuracy and phase angle error of the

PTs (VTs) and CTs. Instrument class 1 or better PTs and CTs are

recommended. Do not use protection class (10P10, etc.) CTs to feed the

power meters; they have poor accuracy and phase characteristics.

Ensure that the CT primary rating has been selected so that your normal

load variation lies between 40% and 80% of its full scale. If your CT is over-

rated, say if the load is always less than 10% of the CT primary rating,

accuracy suffers. On the other hand, if the CT is under-rated, then you may

exceed its full scale and burn out both the CT and the power meter.

PT (VT), CT Wiring

The PTs (VTs) and CTs must have adequate VA rating to support the

burden (loading) on the secondaries. You may want to support the auxiliary

supply burden from one of the PTs (VTs). CT wiring can impose additional

burden (loading) on the CT. For example, if the CT has a 5 A secondary and

the wire resistance is 1.0 Ω, then the CT has to support an additional burden

of 5 VA. If the wiring distance from the CT secondary is greater than stated

in Table 5-5 on page 41, then the CT could get over-burdened and give

large errors. Choosing a 1 A CT secondary can reduce this error. The CT

secondary value must be user programmed into the power meter.

The power meters should be conveniently located for easy connections of

voltage (PT), current (CT) signals, and auxiliary (control) supply.

NOTE: The power meters user programmable PT and CT primary or secondary settings, may

be utilized to Calibrate out the PT and CT amplitude error, for improved accuracy.

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