We are Apogeeweb Semiconductor Electronic


Home arrow Relays arrow What You Need To Know About Induction Disc Relay

arrow left

arrow right

What You Need To Know About Induction Disc Relay

Author: Apogeeweb
Date: 25 May 2022
directional relay



Ⅰ The Types of Disc relay

Ⅱ Principle of Induction Disc Relay

Ⅲ Induction-Disc Relay

Ⅳ Advantages of Induction Disc Relay

Ⅴ Applications of Induction Disc Relay

Ⅵ How you Should Test an Induction Disc Relay’s Pickup

Ⅶ REDI – TM64 – Electronic Disc Relay

Ⅷ The Difference Between a Reverse Power Relay and a Watt Hour Induction Disc Relay



A disc relay is a form of electromagnetic relay that operates on the concept of electromagnetic induction and looks similar to a split-phase induction motor. The interaction of fluxes shifted in time and space in the rotor will produce the operating force (movable element). This article goes over disc Relay in further detail.

Electromagnetic Induction Disc Relay


Ⅰ The Types of Disc relay

The majority of relays are used to protect wires and equipment. There are two types of induction relays: induction disc relay and induction cup relay.

 Principle of Induction Disc Relay

Induction disc relays, like induction motors, work on the principle of electromagnetic induction. The interaction of alternating flux with one of the magnets and eddy currents induced in the rotor (disc) with the other alternating flux produces torque in these relays. Both fluxes have the same frequency, but there will be a phase delay between them. As a result, these relays can only be used on alternating current circuits. The moving element of this relay is a disc to which the relay's moving contact is fixed.

Induction disc relays are of two types. They are,

  • Induction relay with shaded poles,
  • Induction relay of the Watt-hour meter variety.

 Induction-Disc Relay

This was originally employed in the design of electro-mechanical energy meters and was used in the basic implementation of an overcurrent relay. An aluminum disc revolves between the poles of an electromagnet, producing two alternating magnetic fields that are phase and space-separated. The eddy currents generated by one flux and the remaining flux interact to generate a torque on the disc. The flux displacement in early relays was produced by a copper band wrapped around a portion of the magnet pole (shading ring), which displaced the flux contained by it. As seen in Figure 11.14, later designs of these electromechanical relays used a watt metric principle with two electromagnets.


Figure 11.14 Induction-disc relay

The lower electromagnet's current is induced by transformer action from the higher winding, resulting in sufficient displacement between the two fluxes. This, however, can be modified by connecting a reactor to the secondary winding.

The phasor diagram in Figure 11.15 depicts the basic method of action of the induction disc. The torques produced are proportional to F2ij sin a and Fj i2 sin a, hence the total torque is proportional to Fj F2sin an or q i2sin a because F: is proportional to q and F2 is proportional to i2.


Figure 11.15 Operation of disc-type electromagnetic relay, (a) Fluxes, (b) Phasor diagram. i1 and i2 are induced currents in disc

This relay is powered by a current transformer (CT), and the sensitivity can be adjusted using the connector arrangement shown in Figure 11.14. The time it takes for the contacts to close is changed by altering the angle at which the disk must rotate.

Figure 11.16 depicts the operational characteristics. To employ a single characteristic curve for all relay sensitivities (plug settings), a parameter known as the current (or plug) setting multiplier is used as the abscissa rather than the current magnitude, as shown in Figure 11.16. The time multiplier changes the angle at which the disk rotates, translating the curve vertically.


Figure 11.16 Time-current characteristics of a typical induction disc as a function of plug-setting multiplier. TMS stands for time multiplier setting.

Inverse Definite Minimum Time is the name given to this relay characteristic (IDMT). The operating characteristic of a conventional IDMT relay is defined as:

The operating-characteristic-of-a-conventional-idmt-relay

TMS: Time Multiplier Setting PSM: Plug Setting Multiplier


The following example shows how to use this curve (which is often displayed on the relay casing).

Example 11.1

Calculate the operating period of a 1 A, 3 s overcurrent relay with a Plug Setting of 125 percent and a Time Multiplier of 0.6. The supplying CT has a 400:1 A rating, and the fault current is 4000 A.


The fault relay coil current = (4000/400) x 1 = 10 A. The nominal relay coil current is 1.25 A (1 x (125/100). As a result, the relay fault current multiplied by the Plug Setting = (10/1.25) = 8 (Plug Setting Multiplier). The time of operation is 3.3 seconds for a time setting of one, according to the relay curve (Figure 11.16). The time multiplier (TM) regulates the operating time by adjusting the angle at which the disc rotates to seal the connections. 3.3 x 0.6 = 2.0 s is the actual operation time. This can be calculated simply from the equation (11.1)

as:  equation

Induction-disc relays can be made sensitive to real power flow by feeding the upper magnet winding in Figure 11.14 from a voltage and the lower winding from the equivalent current via a potential transformer. Because the top coil has a large number of turns, the current lags the applied voltage by 90°, whereas they are practically in phase with the bottom (small number of turns) coil. As a result, Fj is proportional to V, F2 is proportional to I, and torque is proportional to FjF2 sin a, or VI sin (90 — a) or VI cos a. (where a is the angle between V and I).

The torque direction is determined by the power direction, hence the relay is directional. A power relay combined with a current-driven relay can give directional overcurrent protection.

 Advantages of Induction Disc Relay

  • Induction disc relaysare well-built devices.
  • Under abnormal situations, the operation of the induction disc relay can be easily controlled by simply opening the secondary coil.
  • The current and time settings can be easily obtained by employing induction disc relays.
  • Induction disc relays are dependable and precise.
  • They can be used to defend against overcurrent.

 Applications of Induction Disc Relay

  • Inductiondisc relays are utilized where dependability and robustness are required.
  • These relays have a wide range of applications where slow-speed relays are required.
  • When an adjustable operating time and time-delay feature is required, induction disc type relays are used.
  • This relay is utilized when a high reset to pick-up ratio is required.

Ⅵ How you Should Test an Induction Disc Relay’s Pickup

Technically, you should set the relay to the particular specifications provided in the instruction manual, but doing so has the following drawbacks:

  • They are contradictory, which indicates that various processes are required for different models.
  • They are impracticable for maintenance testing since they require changing the settings and do not demonstrate that the relay is operational at the in-service settings.
  • They do not permit automatic control for more trustworthy results in the absence of external equipment.
  • Two distinct testers will almost certainly produce two different test results.

Use the standard test procedure most testers, and automated test software, perform so that:

  • On all relays, everyone follows identical processes.
  • You will be responsible for ensuring that the relay is operated under normal operating conditions.
  • The test findings can be automated.

Different relay tests are more likely to produce consistent results across maintenance periods.

After all, that's what all the cool relay testers are already doing.

 REDI – TM64 – Electronic Disc Relay

redi – tm64 – electronic -disc-relay

The REDI-TM64 is an electronic disk relay designed to replace old electromechanical relays and the most recent electronic disk relays. The REDI-TM64 is built on a 2o2 microcontroller architecture in diversity, which ensures SIL4 safety. The function of disk relays is to certify the track circuit occupancy status (BTC), that is, to signal whether a train is traveling over a specific rail section. This is accomplished by comparing the amplitude, phase, and frequency of two electrical impulses (local voltage and national voltage).

The existence of real-time microcontrollers enables measurements with a high sample frequency and high accuracy, as well as evaluating the status of the track circuit correctly and safely, even in the presence of large traction current disturbances. A powerful software technique reduces distortion, noise, and disturbance components, resulting in REDI intervention in under 100mS.

The REDI-TM64 has a user interface that allows the device to be customized in the field (power factor correction using a user-configurable offset, self-reflection adjustment) and displays the device's most important parameters (presence of PSK modulation, track circuit status, etc.).

External devices (capacitors) are not required to correct for any phase shift in the field by the REDI-TM64.

The RFI specification DTCDNSSSTB SR IS 21 028 C is met by the REDI-TM64.

The REDI-TM64 provides SIL4 safety according to CENELEC standards 50126, 50129, and 50128.

Ⅷ The Difference Between a Reverse Power Relay and a Watt Hour Induction Disc Relay

What is the difference between a reverse power relay and a watt hour induction disc relay?

Both are disk-type meter relays that are used in large-scale ring feeds to isolate one city from the rest in the case of a catastrophic fault. They operate at staggered intervals and monitor overcurrent and reverse power.


1. What is directional relay?

Overcurrent relays in the power system respond to excessive current flow in a certain direction. The relay is typically made up of two components. A directional element, for example, determines the direction of current flow in relation to a voltage reference.

2. Why directional relay is used?

On buses with two or more sources, directional overcurrent relays are typically utilized on incoming line circuit breakers. They are wired to trip an incoming line breaker to let fault current flow back into the source, ensuring that a failure on one source does not feed the other sources.

3. What is the difference between SSR and relay?

The distinction between Solid State Relays (SSRs) and Mechanical Relays Solid state relays, or SSRs are a form of relay that may be found all over the world. The fundamental distinction between solid-state relays and ordinary relays is that solid-state relays do not have moveable contacts (SSR).

Best Sales of diode

Photo Part Company Description Pricing (USD)

Alternative Models

Part Compare Manufacturers Category Description

Ordering & Quality

Image Mfr. Part # Company Description Package PDF Qty Pricing (USD)

Related Articles


Leave a Reply

Your email address will not be published.

code image
Rating: poor fair good very good excellent

# 0 1 2 3 4 5 6 7 8 9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z