LJ Relays

When the integrity of your system cannot be compromised, the high speed LJ Relay from RPS is the right choice. This high speed auxiliary relay family, designed and manufactured by RPS, has a high inertia to mechanical shock and electrical transients and a patented coil that ensures that this rugged relay is immune from false trips – without compromising trip speed.

Trusted to get the job done, the maintenance free LJ has been installed in thousands of high voltage substation and heavy duty industrial applications across North America and has been providing reliable protection and trouble free service for more than 30 years.

A variety of device mounting, faceplate and contact configurations are available – making the LJ Relay ideally suited for both new installations and retrofit applications.

Compare the LJ high speed auxiliary relay to relays like the ABB AR, Alstrom Prima, Alstrom MJAV and GE SBA series relays. The LJ relay offers one of the fastest operating speeds and the highest inertia auxiliary relay immune to electrical transient and immune to mechanical shock miss-operations. The LJ relay is made in the USA. For complete technical details, click here.

FEATURES LJ RELAYS
ABB AR
ALSTOM MJAV
ALSTOM PRIMA
Available Contacts 2, 6, 10 4 5, 10, 20 4
Operating Voltage 48, 125, 250 VDC 48, 125, 250 VDC 24, 30, 48, 110, 220 VDC 24, 30, 48, 110, 220 VDC/VAC
Operating Time 4 msec for 6 contact model
5msec for 10 contact model
4 msec for 4 contact
(high threshold) model
8 msec for 5 & 10 contact
model 10msec for 20 contact model
25msec
Contact Current Carry Rating Continuous= 5 Amps DC
Short Time= 30 Amps
Continuous= 3 Amps DC
Short Time= ?
Continuous= 5 Amps DC
Short Time= 30 Amps
Continuous= 10 Amps DC
Short Time= 30 Amps
Contact Current Interrupt Rating Resistive= 1.1 Amps @ 125VDC Resistive= 0.5 Amps @ 125VDC Resistive= 0.64 Amps @ 125VDC Resistive= 0.96 Amps @ 125VDC W/Magnetic blow out= 2.8 Amps
Estimated Delivery 3-4 weeks 3-4 weeks 16-18 weeks 16-18 weeks

 

Technical Overview

The LJ relay is a family of high speed auxiliary relays used in protective relay schemes for ultra-fast tripping of circuit breakers. The relay is also used to provide isolation of primary and back up relays. The LJ relay has the fastest operating speeds for the number of available contacts. Other relays like the PRIMA relay is more of a general purpose control relay due to its slower speed and time delayed operation/reset options. The PRIMA relay with magnetic blow-out contacts have a greater current (resistive & inductive) interrupting rating than the LJ relay. However, when used for tripping circuit breakers this is typically not an issue since 52a contacts interrupt the trip coil current and not the LJ relay trip contact. The LJ and AR relays have optional test switches that isolate relay coil and contact output circuitry. Alstom relays have no test switches.

The LJ relay family offer a broad variety of flush and projection mounting styles in dustproof, aluminum cases. The LJ relay offers the highest inertia auxiliary relay – making it immune to electrical transient and mechanical shock miss-operations. Made in the USA, the LJ relays normally delivery in 3 to 4 weeks upon receipt of order, not months as is the case with several brands.

 

The LJ Relay is a high speed auxiliary relay, designed and manufactured by RPS for more than 30 years, offers a variety of device mounting, face plate and contact configurations for both new installations and retrofit applications.

Benefits of the LJ design include:

  • 4 millisecond operate time
  • 6 or 10 usable, easily configurable contacts
  • Immune to miss-operation from severe vibration or mechanical shock
  • Patented shielded coil provides immunity to misoperation from system transients while reducing internally generated transients to a very low level
  • Individually sealed contacts do not require cleaning or adjustments
  • Available with integrated contact isolating switches
  • Relays and contacts are sealed from fly ash and other contaminates
  • Available with direct driven, manually resettable target
  • Up to 50% panel space savings over competitive units
Ordering Guide

Modern Electromechanical Relay Applications

APPLICATION 1: Transients in Control Circuits

Problem – Electric utilities use shielded control cables to minimize transients in control circuits and μP relays are designed and tested to withstand transient voltages. However, an additional consideration is that the rapid response and low energy requirements of μP relays has resulted in unwanted DTT (Direct Transfer Trip) actuations when trip signals are wired directly to μP relays. In fact, utilities purchasing LJ relays have reported that transients in control scheme wiring have actually resulted in unwanted DTT actuations.

Solution – Place high speed LJ relays near μP relays and to use high speed LJ relays to serve as a buffer between wired inputs and μP relays.

This is illustrated in Figures 2 & 3 for Conshohocken and Wyomissing Substations. In this application, Wyomissing Substation is not equipped with 138 KV fault interrupting devices and DTT is needed to trip the 138 KV circuit breaker at Conshohocken in the event that a transformer failure occurs at Wyomissing.

APPLICATION 2: Remote Lockout Reset

Problem – Substations that are equipped with two, three, or more large power transformers, simultaneous actuation of multiple lockout relays is beyond design basis and can result in a significant number of customer interruptions.

Solution – When faced with this possibility, some utilities have chosen to install LJ relays with remote reset capability rather than traditional, hand reset, lockout relays for transformer and bus differential relaying schemes. This application allows operators to quickly restore service to customers, using supervisory control, if multiple components trip out simultaneously.

This is illustrated in Figures 4 and 5 for Conshohocken Substation where LJ relays are actuated by Transformer T12, Transformer T14, Bus 1, Bus 2, and Bus 3 differential relays to trip circuit breakers when a fault occurs.

This remote reset feature allows operators to restore a transformer or bus to service when substation video images do not show signs of arcing and damaged insulators, sudden pressure relays have not actuated, and other indicators of component failure are not evident at the remote power control center.


APPLICATION 3: Contact Multiplication

Problem – Substations that are equipped with protective relays that have limited trip output contacts, such as electromechanical bus differential relays.

Solution – The LJ relays can serve as a contact multiplier. LJ relays are ideal for this application as the rated contact closing time is 4 ms.

This application is illustrated in Figure 6 where a bus differential relay for Bus 2 actuates an LJ relay that trips the two sectionalizing circuit breakers that are connected to Bus 2 (shown in Figure 4).

EM Relay Technology’s Part in Modern T&D Protection

Safe and reliable electric power at a reasonable cost is the goal of any electric utility. How this goal is achieved has improved over the years. Many of the improvements were driven by enhancements in the world of protective relaying systems, as the electric utility industry went from using Electromechanical Relays (EM) to Solid State Relays (SSR) and then to Microprocessor based Relays (μP). And as the technology evolved, the industry has benefited – as witnessed by constant improvements in two common metrics – the System Average Interruption Duration Index [SAIDI] and the System Average Interruption Frequency Index [SAIFI].

However, during this technical and performance evolution, companies like Relay & Power Systems (who makes a specialized EM relay called the LJ Relay that is used in many thousands of power systems throughout North America) have seen continued and increasing demand for the older EM technology.

How can this be? Why is there continuing interest in mature EM technology such as the LJ relay?

RPS has recently interviewed several utility users and learned that EM relays like the LJ provide a prudent alternative for a wide variety of power system configurations challenges. One user in particular, a major northeast electrical utility, was instrumental in working with RPS (then known as Relay Associates) in the development and evolution of the LJ relay several decades ago. This utility user shared a few applications for which they use the relay today.

Substations that are equipped with two, three, or more large power transformers, near simultaneous actuation of all lockout relays is beyond design basis and may result in a significant number of customer interruptions. When faced with this situation, some utilities have chosen to install LJ relays rather than traditional lockout relays for transformer and bus differential relaying schemes. This application allows operators to quickly restore service to customers using supervisory control in the unlikely event that multiple components trip out almost simultaneously (See Figure 1).

Illustration of Transformer T12LJ Application

When transformers are tapped directly off transmission lines, Direct Transfer Tripping (DTT) is installed to trip remote circuit breakers. In addition to the simultaneous trip concern that could trip remote circuit breakers as well as local circuit breakers, a second concern is that transients at the local substation could cause a direct transfer trip signal to be sent to the remote substation. In this case, LJ relays, which have high energy input requirements, are installed between the initiating device and the DTT transmitter (See Figure 2)

This is illustrated in Figure 2 for Jamestown and Williamsburg Substations as Jamestown Substation is not equipped with 138 KV fault interrupting devices.

In some high transient environments/conditions the rapid response and low energy requirements of μP relays has resulted in unwanted DTT (Direct Transfer Trip) actuations when trip signals are wired directly to μP relays. One solution is to place high speed LJ relays near μP relays and to use the high speed (4ms), transient resistant nature of EM relays like the LJ to serve as a buffer between wired inputs and μP relays.

As power systems continue to evolve and customer expectations for high quality, dependable power continues to increase, proven EM relay technology like the LJ are providing a prudent alternative that can do their small part to help utilities cost effectively and reliably achieve their SAIDI and SAIFI goals.

 

For the LJ Relay manual, which includes detail specifications and order guidelines, click here.