Ic Ib Ia Va Vb Vc - Landis+Gyr

Landis+Gyr
Application Note
05-0320-1
Product:
MAXsys meters and other Transformer Rated Meters
Subject:
Information on the wiring of Instrument Transformers
Date: 03/20/2005
Background Information
Warning this is to be used for information only. This is not a
recommendation or instructions on how to wire Instrument
Transformers or Meters. Only trained Meter Technicians with a
good understanding of Instrument Transformer Rated meters
should ever work on metering circuits and then they must always
follow their company’s safe work practices. Mistakes in wiring
Instruments Transformers can cause damage to equipment and
death to personnel.
To understand applications using instrument transformers it is important
(necessary) to understand the polarity markings on the transformer as well
as following your company’s safety guide lines when wiring instrument
transformer rated power instrumentation. You may have heard the term,
with current in on polarity, you will get current out on polarity (they were
saying the signals would be the same). To help understand the polarity
markings when looking at instrument transformers, you will find on the
high side (primary) and on the low side (secondary) of the transformer a
polarity mark. The best way to think about this, is the polarity marks are
two points on the same wire, from the stand point the signal going in on
polarity will be the same signal you see coming out on polarity from a
phase relation, the signals will be in phase with each other (look the
same), only the magnitude of the signal will change. If you think about just
one VT and CT it maybe easer to see what happens. With the polarity
terminal of the VT (high side) connect to the Line and the polarity terminal
on the CT (high side) facing the source and the polarity terminals on the
low side of the transformers connected to the “Vin” and “Iin” of the meter
and with power flowing from the source to the load the meter will register
in the delivered direction (you could say the voltage and current are in the
same phase (direction). When the power starts flowing from the load to
Landis+Gyr Inc.
2800 Duncan Rd. Tel: (800) 777-2774
Lafayette, IN 47904-5012 Fax: (765) 742-0936

Landis+Gyr
Application Note
05-0320-1
the source, the voltage signals remain the same however, now the current
is flowing into the non-polarity side of the transformer and now the current
signal has now moved by 180 degrees and the meter starts registering in
the received direction.
With this basic understanding we can look at three possible ways to install
Instrument Transformers and connect them to a three element meter.
Please remember there are many ways to connect transformers to a meter
and get the same results. We are only going to look at three installations.
The first one is a 4 wire wye and the last two will be on 3 wire Delta. This
to help you understand the connections, it is NOT intended to be used as a
meter wiring diagram. Warning because each company has its own
grounding practices for instrument transformers, no grounds are shown in
any of the illustrations.
Landis+Gyr Inc.
2800 Duncan Rd. Tel: (800) 777-2774
Lafayette, IN 47904-5012 Fax: (765) 742-0936

Landis+Gyr
Application Note
05-0320-1
Illustration 1 represents a full 3 element meter. This will be used as a
reference in illustrations 2-4.
Illustration 1
Va Vb Vc Ia Ib Ic Ic Ib Ia Vc Vb Vc
In In In In In In Out Out Out Out Out Out
Va Vb Vc Ia Ib Ic Ic Ib Ia Va Vb Vc
In In Out Return Out Return
Landis+Gyr Inc.
2800 Duncan Rd. Tel: (800) 777-2774
Lafayette, IN 47904-5012 Fax: (765) 742-0936

Landis+Gyr
Application Note
05-0320-1
Illustration 2 represents a 4 wire Wye installation.
With the connections below the delivered registers will increase when
power flows from the source to the load. Note: with the VT’s being
installed on the source side of CT’s, they will not be seen as load to the
metering system.
Illustration 2
SOURCE
N A B C
V
T
To (Va in) meter
To (Va out) meter or return
V
T
V
T
To (Vb in) meter
To (Vb out) meter or return
To (Vc in) meter
To (Vc out) meter or return
C
T
To (Ia in) meter
To (Ia out) meter or return
C
T
To (Ib in) meter
To (Ib out) meter or return
C
T
To (Ic in) meter
To (Ic out) meter or return
LOAD
Landis+Gyr Inc.
2800 Duncan Rd. Tel: (800) 777-2774
Lafayette, IN 47904-5012 Fax: (765) 742-0936

Landis+Gyr
Application Note
05-0320-1
Illustration 3 represents 3 wire Delta installation. We use the same
polarities in this example as we did in illustration 2. When using a three
element meter like the MAXsys meter you would only use the “A & C”
elements. With the MAXsys meter you would leave “B” currents open and
connect “Vb in” to return (you can also leave the voltage connect open.
Illustration 3
SOURCE
A B C
V
T
To (Va in) meter
To (Va out) meter or return
V
T
To (Vc in) meter
To (Vc out) meter or return
C
T
To (Ia in) meter
To (Ia out) meter or return
C
T
To (Ic in) meter
To (Ic out) meter or return
LOAD
Landis+Gyr Inc.
2800 Duncan Rd. Tel: (800) 777-2774
Lafayette, IN 47904-5012 Fax: (765) 742-0936

Landis+Gyr
Application Note
05-0320-1
Illustration 4 represents 3 wire Delta installation. We use the same
polarities in this example as we did in illustration 3, EXCEPT the polarities
on the “C” phase VT has been reversed, by reversing both the primary and
secondary connections we end up with the same signals. When using a
three element meter like the MAXsys meter you would only use the “A & C”
elements. With the MAXsys meter you would leave “B” currents open and
connect “Vb in” to return (you can also leave the voltage connect open).
Illustration 4
SOURCE
A B C
V
T
To (Va in) meter
To (Va out) meter or return
V
T
To (Vc out) meter or return
To (Vc in) meter
C
T
To (Ia in) meter
To (Ia out) meter or return
C
T
To (Ic in) meter
To (Ic out) meter or return
LOAD
Landis+Gyr Inc.
2800 Duncan Rd. Tel: (800) 777-2774
Lafayette, IN 47904-5012 Fax: (765) 742-0936