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C ONSTRUCT I ON

OFA

TYPE ON AUTOILATIC NETWORK RELAY

DELIOI‘TSTRJ T ION BOARD
FOR

A. C . LABORATORY

trj

OF TE
III C :1 I GAE? STATE C OLLEGE

A THESIS
SUBA’IITTED TO TEE- FACULTY
OF THE

.‘JI I C :1 I GAE? STA T E C OLLEG-E

BY
J . IOLISELLR

‘4'
..Io J

. HARSHALL
h—q
CANDIDATES FOR DEG-REE OF

BACHE OR OF SCIEZ‘ICE

JUNE 1930

THESIS

 

Introduction ___________________________

Automatic Network Type CE Relay
Application _____________________
Construction ____________________

Operation .......................

Automatic Network Relay Board
Construction ---—--———-——-___-_-_

Operation ______________________ ..

1033‘?O‘c3

Page

3

__ 5
__ 6
10

__1 5
__20

INTRODUCTION

The object of this thesis is to provide a labor-
atory method of demonstrating the application and the
Operation.of the automatic network relay.

This is accomplished by the construction of a por-
table switchboard provided with the required number of
relays and auxiliary equipment and using in conjunction
with this the standard laboratory sources of energy and
load. The principle of design is the result of deducing
a complicated network system to a simple laboratory arr-
angement still embodying the fundamental characteristics
of the network relay.

In the general sense of the word, the relay'is a-
device which Opens or closes a local circuit under pre-
determined electrical conditions of the main circuit.
The important functions of the relay are,(I) to protect
the main circuit,(2) to regulate the current in the main
oircuit,(3) or to signal,the conditions of the main cir-
cuit. The automatic network relay falls under the first
class, because it automatically protects the main circuit
from being damaged by short circuit currents. However in
its use on the demonstration board it acts as a signal-
ing device showing the existing conditions of the main
circuit. In the case of a short circuit the Operator

must Open the main line switch in order to provide the

necessary protection.

There are many types of protective relays used in
both a. c. and d.c. work. They are built to furnish pro-
tection against over-voltage, no-voltage, over-load, no-
load, reverse power and reverse phase. They may Operate
either directly or in connection with other relays . The
relay may operate instantaneous, it may have a definite
time duration, or it may have a time delay inversely pro-
portional to the extent of the overload.

Many combinations of the types and the character-
istics of relays may be secured. The kind of application
that is necessary in almost any electrical system can;
be furnished by using one or more of these combinations.

In the Operation of a distribution network it is
not necessary that the automatic network relay have the
lover-load type of protection. There is an over-load ad-
Justment on the main circuit breaker in the transformer
primary circuit that will cause the transformer to be-
come disconnected from the feeder in the case Of an
over-load. (The position of this breaker can be seen by ‘
refering to Plate 2A.)The network type relay, however,
is designed with the reverse power,the reverse phase,
and the under-voltage systems of control. With these
functions the automatic network relay provides all the

protection that is necessary for a low-voltage distribue

tion system.

APPLICATION

The type CN relay is used primarily as a protective de-
vice for low-voltage,AC,distribution networks. The relay
insures continuity of service for large distribution systems
in the larger cities Where many feeders are interconnected
to form the network.

A loop or ring network consist of a number of high vol-
tage feeders each of Which feed a number of banks of distri-
bution transformers. The transformers feed into an intercon-
nected low tension secondary network. The Operation of such
transformers in parallel,on both primary and secondary sides,
has many advantages but in case of a fault serious results
may occur before the transformers can be disconnected by
hand Operated devices.

Such loop systems make it necessary to provide some pro-
tection against high voltage feeder faults and short circuits.
Also the necessity of a device to connect the distribution
transformer to the network When needed and also to disconnect
the transformer when the load is low or in case of reverse
energy flow. In such cases the reverse power protection
should operate on values as low as the magnetizing current
of the distribution transformer. The circuit should not be
Opened under direct flow and should close the circuit when
the voltage and phase relationships are satisfactory.

The type CN automatic network relay is designed for

such protection and Operating characteristics.

This type of relay is placed between the distribution
transformer and the network. It insures continuity of ser-
vice on the network by serving to disconnect any of the fee-
ders which develops a fault thus preventing the tripping out
of the other feeders by overload protection.

The network relay insures a constant voltage on the net-
work as additional distribution transformers are connected in
automatically when the load becomes such as to cause a voltage
drOp of more than one4half volt.

It also insures the most economical working of the reser—
ve distribution transformer as it is connected to the network

only when the ones already connected become overloaded.
CONSTRUCTION

The network relay shown in Plate 1 Operates on the in-
duction principle. The rotating element is a OOpper disc. The
lower end of the shaft on which the disc is pressed is a har-
dened and polished steel pivot with a round end. This pivot
runs on a cup shaped jewel. There is a bushing in the top of
the screw carrying the jewel which prevents the pivot from ri-
ding up on the curved sides of the jewe1,causing the disc to
tilt and perhaps bind in the air gap under the heavy torque
conditions to which it is often subjected. Since there is on-

ly a few thousandthe of an inch clearance between the bushing

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HATE / WNW/VG DIAGRAM OF TYPE C/V AUTOMATIC RELAY

and the shaft the possibility of dirt or other foreign mat-
ter getting on the jewel is greatly reduced. The upper bea-
ring is of the pin type.

All contacts are made of pure silver. The moving con-
tacts of the relay are mounted on a counter shaft which is
geared to the disc shaft. The counter shaft is covered with
a moulded insulation hub on which the moving contacts are
fastened.

The gears used have special teeth to prevent the gears
svsr coming out of mesh. When the relay is de—snergized the
moving contact is held firmly against the stationary contact
by means of a spiral spring. The inner end of this spring
is fastened to a spring adjuster. This spring adjuster al-
lows the initial tension of the spring to be changed with-.
out changing the strength of the spring. The travel of the
moving contact is limited by a small aluminum stop riveted
on the disc. The maximum contact Opening is slightly more
than one-sixteenth of an inch. This is sufficient to pre-
vent the contacts accidentally closing even when the relay
is subjected to extremely heavy jars or vibrations. The
stationary contact is mounted on a flat,phosphor bronze
spring. A spacer is placed behind the spring which allows
it to deflect approximately one—sixteenth of an inch. On
tOp of this spring is another spacer and then a guard to
prevent the contacts from closing before they should. The

complete assembly is mounted on an insulated block.

In order to secure the prOper Operationof the relay un-
der sudden changes of voltage and current a certain amount
of damping is necessary. This is secured by means of a per-
manent magnet.

The main contacts of the network relay do not control
the operating circuit of the network protector. The auxil-
iary contactor Operates the network protector. It is a small
AC cOntactor controlled by the main contactor. It has a lam-
inated iron circuit with a permanent air gap.

The laminated iron circuit of the main electro-magnet is
made in two sections. Three coils are on the lower punchings,
the potential coil is for 120 volts and two auxiliary current
coils of a few turns of heavy wire are connected in series
with the current coils. The current coils are wound on the
upper part of the electro-magnet. The phasing and holding
coils are of fine wire placed on each of the poles of the up-
per pole assembly. The complete relay is mounted on a rectan-

gular cast iron base with a glass cover as shown in the picture.

141+.

 

OPERATION

The Operation of the network relay is best described by
referring to Plate 8. This simplified connection diagram of
the relay makes its operation more easily understood. It
shows the internal connections of the relay and also the way
in which it's various circuits are connected to the network.

The control circuit,terminals 1&2,have been Omitted in
order to simplify the picture.

In a low voltage network when all feeders connected to
the low voltage network are Open the relay will be complete-
ly de—energized and its main contacts will be held in closed
position by the spiral spring. If the circuits breakers at
the substation are closed energizing the transformers, the
holding coil circuit will have full potential on it. The
phasing circuit is also energized. Although current is flo—
wing through the phasing coil no torque is produced because
the potential coil is de-energized. The coils on the upper
poles of the electro—magnet cannot produce torque except
when energized in conjunction with potential. The phasing
circuit always has full potential on it. This is equal to
the vector difference of network voltage and the secondary
voltage of transformer.

When the network voltage is lower than the feeder vol-
tage the voltage across the phasing circuit is increased and

also the closing torque of the relay.

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12

As soon as the contacts of the relay are closed by the tor-
que produced by the potential and phasing coils an addition-
al torque is produced by the holding coil. This prevents

the contacts from chattering. After the current flows into
the network a part of it passes through the current coil
Which is connected across a reactive shunt. This current
produces a closing torque in addition to the others. The
network breaker will remain closed even if the voltage conr
ditions change so that there is no current flowing'because
the holding coil still produces a torque large enough to hold

the relay contacts closed.

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Using the figure above, if one of the circuit breakers
at the station is Opened,magnetizing current will flow from
the network to the transformer. This current will cause the

contacts to Open and disconnect the circuit breaker.

13

The action of the relay is just the same if a fault develops
in the transformer or feeder,except the Opening torque will
be much greater. The relay should operate quickly so as to
reduce the disturbance caused when a fault occurs.

The fact that the network relay must Operate on very small
values of current and also on very large values without over-
heating made it necessary to use a reactive shunt. At very
small values of current the reactance of the shunt is high
land therefore a large part of the current will pass thru the
current coil. For large values of current the reactance of
the shunt decreases and only part of the current will flow
through the current coil.

The phasing coil is so designed that it will Operate the
relay with one volt impressed on it. But at times it may also
have full potential on it. In order not to have full poten-
tial on it a phasing lamp is put in series with it. Figure
on Plate 3 shows a characteristic resistance-voltage curve

of a phasing lamp.

THE NETWORK RELAY BOARD

In studying the Operation and the characteristics of the
network relay it seems almost impossible to use such a relay
in a laboratory. In the first place the relay is designed to
Operate under conditions of load ranging from 1oo-5eo amperes.
In the laboratory a maximum of about 85 amps is all that can
be used because of the size of the equipment. Again the net-
work relay is designed to operate a loop network. Such a
complicated loop can be found only in an outdoor distribution
system. Our design is the result of deducing a complicated
network system to a simple laboratory arrangement.

Now in the laboratory where this demonstration board is
to be used,there are two similar transformers that have a
common primary source of energy supply. These two transfor-
mers are the ideal requirements so that the power can be se-
cured from two points on the network.

The switchboard is constructed as shown in Plate 5. The
energy supply is three phase,60 cycle,llo volts. The relays

are placed on the relay board as shown in the photograph-

15

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The relays are connected to the phases as shown in Plate 4.
In this drawirg the three phase single throw switch is hand
Operated. In practice this switch is an automatic one. In
our design the auxiliary contactor,instead Of Operating the
automatic switch Operates a pilot light.

In the simplified network there are several lamps placed
in the center of each half of the loop. These lamps are im-
‘portant as they aid in keeping the load equalized.

The board is provided with two auxilliary switches that
serve to provide the use Of two alternators in place of two
transformers.

The method of wiring the simplified loop on the relay
“board is shown by plate 5. The wiring connections for the
two sets of relays is shown in Plate 4. This plate illus-
trates the connection of the pilot lamp in the relay cir-
cuit, also the position of the reactive shunts in the main
supply lines. Temporary connections are provided in the
construction so that the reactive shunts may be readily re-
moved and replaced whenever necessary.

Referring to Plate 5 the twelve lamps in the loop are
Of the 25 watts, 110 volts type. The two pilot lamps are

15 watts, 110 volts.

17

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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20

OPERATION

The operation of the relay demonstration board is best
described by referring to the above figure. This firgure is

a single wire diagram of the three phase circuit.

A. With Transformers as Supply.

In order to run a complete test on the Operation of these
relays it is necessary that an induction regulator be placed
in the line (B), between the laboratory switch panel and the
relay.

The two transformers are connected to the relay board
by means of jumpers. Switches A and B are open and auxil-
liary switches #1 and #2. Close the auxilliary switch #1.
The load leads can than be connected in. Then close the
main switch A and a small load is placed on that half of the
loop network. As long as the induction regulator in in neu-
tral position the pilot lamp B will light, showing that
switch B may be closed. This action will not take place
however unless the voltage of the network is slightly less
than that at the line side of the switch B. The phase se-
quense must be correct also before the pilot lamp will light.

Once the transformer B is connected to the network the
load on A can be increased and a load also placed on part
B'equal to it. The two transformers will only carry the load
that is in their half of the loop due to the impedance of the

lamps in the center of the lOOp.

21

This type relay will indicate an Opening Of the hand op-
erated switch only in case of reverse power flow. This ac-
tion may be accomplished by rotating the induction regulator
until it actually receives power from the network and causes
current to flow in Opposite direction through the relay.

The reverse current will only be equal to magnetizing cur-
rent of the regulator. This however will be large enough to
cause the relay to function and the pilot lamp to go out.
The switch B should than be opened. As the induction regu-
lator is rotated to zero position the pilot lamp will re-
light and the switch B can be closed. The relays Operate
only when their is a difference of potential across the

main switches.

B. With Alternators as Supply.

The power supply can also be the alternators G-7 and G-8.
When alternators are used they must be similar.

Connect the energy supply and the load to the relay board.
Close auxilliary switch # 2, keeping auxilliary switch #1 open.
The test is than carried out as in the case of the transformers.
The load in this test is not separated by high impedance as it
was in the former test. Either side made be loaded or both.

When alternators are used the machines may be adjusted so
that one will receive power from the other. This action will

cause the reverse power function of the relay to work.

 

 

 

 

22

26

BIBLIOGRAPHY.
RELAY HANDBOOK --------- National Electric Light Association.
Type CM Relay Instruction Book -------- WestinghouSe.
Relays ---------------------------------------- Todd.

General Flectric Co. Pamphlet-KC 60031 ---Gen. Electric Co.

Recent Developments in Automatic Network Relays--E1ect. Jl.'27

 

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