TYPES I R P, I R C AND I R D R E L AYS
accurately position the lower pin b earing, which is
mounted on the frame , with respect to the upper pin
bearing , which is threaded into the bridge . The elec
tromagnet is secured to the frame by four mounting
screws.
The moving eleme!'lt assembly consists of a spiral
spring, contact carrying member, and an aluminum
cylinder assembled to a molded hub which holds the
shaft. The shaft has removable top and bottom jewel
bearings.
The shaft rides between the bottom pin
bearing and the upp er pin bearing with the cylinder
rotating in an air gap formed by the electromagnet and
the magnetic core.
The bridge is secured to the electromagnet and
frame by t wo mounting screws. In addition to holding
the upp er pin bearing, the bridge is used for mounting
the adjustable stationary contact housing. The sta
tionary contact housing is held in position by a spring
type clamp.
The spring adjuster is located on the
underside of the bridge and is attached to the moving
contact arm by a spiral spring. The spring adjuster
is also held in place by a spring type clamp .
With the contacts closed, the electrical connec
tion is made through the stationary contact housing
clamp, to the moving contact, through the spiral spring
out to the spring adjuster clamp .
Switch
The auxiliary switch is a small solenoid type
d.c. switch.
A cylindrical plunger, with a silver
disc mounted on its lower end, moves in the core of
the solenoid.
As the plunger travels upward, the
disc bridges the silver stationary contacts. A tapped
resistor is used to enable one to use the contactor
switch on a
24, 48 ,
1 25
or
250
volt d.c. system con
nected per Fig.
23
. The operation of the CS- 1
switch is controlled by the directional unit (D) which
in turn directionally controls the time-overcurrent
unit (CO). When s ufficient power flows in the tripping
direction, the CS- 1 switch operates and bridges the
lag coil of the time-overcurrent unit (CO) permitting
this unit to operate.
I n stan taneo u s O vercurrent U n i t ( 1 )
The instantaneous overcurrent unit is similar in
construction to the directional unit. The time phase
relationship of the two air gap fluxes necessary for
the development of torque is achieved by means of a
capacitor connected in series with one pair of pole
windings.
The normally-closed contact of the directional unit
is connected across one pair of pole windings of the
instantaneous overcurrent unit as shown in the in
ternal schematics. This arrangement short-circuits
the operating current around the pole windings; pre-
venting the instantaneou s overcurrent unit from de
veloping torque. If the directional unit should pick
up for a fault, this short-circuit is removed, allowing
the instantaneous overcurrent contact to commence
closing almost simultaneously with the directional
contact for high speed operation. Total operating
times are shown in Figs.
17
and
1 8 .
In stantaneo u s O vercu rrent U n i t T ra n s fo rm e r
This transformer is o f the saturating type for
limiting the energy to the instantaneous overcurrent
unit at higher values of fault current and to reduce
C.T. burden. The primary winding is tapped and these
taps are brought o ut to a tap block for ease in chang
ing the pick-up of the instantaneous overcurrent unit.
The use of a tapp ed transformer provides approximate
ly the same energy level at a given multiple of pickup
current for any tap setting, resulting in one time curve
throughout the range of the relay.
Across the secondary is connected a non-linear
resistor known as a varistor. The effect of the varis
tor is to reduce the voltage peaks applied to the over
current unit and p hase shifting capacitor.
C H A R A C T E R ! S T I C S
The time characteristics of the directional over
current relays are designated by specific numbers as
indicated below (e.g. ,
IRV-8).
T i m e
C h aracteri st i e s
Short Time
Long Time
Definite Time
Moderately Inverse Time
Inverse Time
Very
Inverse Ti me
Extremely Inverse Time
D e s i gnation
2
5
6
7
8
9
1 1
The relays are available i n the following current
ranges:
Instantaneous Overcurrent Unit (I)
Range
T
a
p
s
0. 5-2
Amps
0 . 5
0. 75
1 . 0
1. 25
1 . 5
2
1-4
1 . 0
1 . 5
2 . 0
2.5
3. 0
4 . 0
2
-
8
2
3
4
5
6
8
4- 16
4
6
8
9
12
16
10-40
10
1 5
20
24
30
40
20-80
20
30
40
48
60
80
5
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