Overload relay is the one of important device for motor control. It can prevent our motor from overheat or winding burning due overload of ampere. We need to setting the value of overload relay properly depend on our application and motor full load ampere.
If we setting low from FLA,it can cause motor trip c0ntinues and process not running smoothly. But if we setting to high from FLA,the overload relay cannot protect the motor if overload happen. It can cause the motor failure or winding burns. So we must calculated and get a right setting for the overload relay.
For adjustable protective devices, In corresponds to the value set. But it is depend on operation and functional of motor. For more detail setting,please refer manual guide of motor from manufacture. We also can setting overload relay value depend on value of service factor motor. Example if service factor 1. Normally,overload relay have this 2 reset function selection. We can choose manual or automatic reset after it trigger overload from motor.
PSM and TMS Settings Calculation of a Relay:
I recommended for manual reset function because we can know when it trip and we can troubleshooting the root cause for tripping issue. So after we found the root cause,we can reset back the overload relay and can continue the operation. I will give you one answer please check whether thwt is correct or not?
While increasing the relay setting of the air circuit breaker no need to switch off the circuit breaker. If we want to decrease the relay setting means we have to switch of the circuit breaker is it correct if this is wrongmeans plese give me correct idea and what is the actual reason and correct answer. Regards Gopalthulasidoss. I was wondering why my overload relay in an air compressor with a star delta starter is downsized compared to the motor fla? If air-compressor still running :- 1 check your overload relay condition.
Perform test trip to ensure it is function properly,if not change it. If your compressor always trip :- 1 Use your actual FLA value and make calculation and set a new setting for your overload relay.
Dear Sir i would like to inform you i need electrical easy formula. Hi Rajendratiwari, In my blog,i already discuss about electrical calculation,Please find my post. I also create Electrical Formulas Categories for basic formula and calculation. Please click link for Voltage drop and Cable sizing calculation. I hope it can help you to understand basic calculation. How to check the functionality of Over Load relay without connect the load May be by control circuit testing.
This process available only at Lab test. My question is 1 is the overload setting too high? Can I say minimum value of overload setting cannot lower than Dear sir Am very pleased finding were we can share knowledge about electrical engineering.
Overload relay setting and calculation
How can i calculate the overload protection for this compressor. For your application : 0.These terms or parameters are not so used in Numerical Relays but they are conceptually used and incorporated in Numerical Relays too but the way of their implementation is quite different than that of Electromechanical Relays.
As we know that an Electromechanical Relay has a coil which when energized, operates the Relay to have contact changeover. But there shall be some minimum current which when flows through the Relay coil, produces enough magnetic force to pull the lever to make contact change over.
Yes, if you ever get a chance to see electromechanical relay, you will observe that there is a flapper kind of thing which is attached with the lever. The lever in turn is attached with contacts.
Thus when a specified current flows through the relay coil, then only it will produce enough magnetic pull to attract the flapper and lever to operate the Relay. A simple picture of relay demonstrating its construction and operation is shown in figure below. This minimum current in the Relay coil at which Relay starts to operate is called Pick-up Current.
On contrary, if the current through the Relay coil is more than the Pick-up current, Relay will operate. In industries, we normally perform Relay Pick-up and Drop-off Test to check the healthiness of relays. Hope your concept of Pick-up current of Relay is clear now.
Now we will move on to Current Setting of electromechanical relays. Current Setting of Electromechanical Relays: Current Setting of relay is nothing but adjusting its pick-up value. Thus we can say that. The plug or tapping is provided on the Relay Coil so that changing the position of Plug changes the number of turns of the relay coil as shown in figure below.
Assume that Current Setting or the position of plug is at 5 then. A Relay is generally provided with control to adjust the time of operation of the Relay.
Normally a Time Setting Dial is provided which is calibrated from 0 to 1 s in step of 0. For practical exposure, let us consider a relay as shown in figure below. Please Zoom the image to clearly view every part of the Relay for better understanding.The basic element in overcurrent protection is an overcurrent relay.
This relay is referred as definite instantaneous overcurrent relay. The relay operates as soon as the current gets higher than a preset value. There is no intentional time delay set.
Overcurrent & Earthfault Protection – Basic Concept:
There is always an inherent time delay of the order of a few milliseconds. The relay setting is adjusted based on its location in the network. The relay located furthest from the source, operates for a low current value. In the feeder with small impedance, distinguishing between the fault currents at both ends is difficult and leads to poor discrimination and little selectivity at high levels of short-circuit currents.
In this type, two conditions must be satisfied for operation trippingcurrent must exceed the setting value and the fault must be continuous for at least a time equal to the time setting of the relay. Thus, is has a time setting and pick up adjustment. Modern relays may contain more than one stage of protection each stage includes each own current and time setting. The settings of this kind of relay at different locations in the network can be adjusted in such a way that the breaker closest to the fault is tripped in the shortest time and then the other breakers in the direction toward the upstream network are tripped successively with longer time delay.
Definite time overcurrent relay is used as a backup protection of distance relay of transmission line with time delaybackup protection to differential relay of power transformer with time delay and main protection to outgoing feeders and bus couplers with adjustable time delay setting. In this type of relays, operating time is inversely changed with the current.
So, high current will operate overcurrent relay faster than lower ones. The operating time of both overcurrent definite-time relays and overcurrent inverse-time relays must be adjusted in such a way that the relay closer to the fault trips before any other protection. This is known as time grading. The difference in operating time of these two relays for the same fault is defined as discrimination margin. The adjustment of definite-time and inverse-time relays can be carried out by determining two settings: time dial setting and pickup setting.
The time dial setting adjusts the time delay before the relay operates whenever the fault current reaches a value equal to, or greater than, the relay current setting. Search for:. Premium Membership. More Information. Relay control and protection guides. The Basics Of Overcurrent Protection. Overcurrent relays The basic element in overcurrent protection is an overcurrent relay. Example, when the overcurrent relay is connected to the end of distribution feeder it will operate for a current lower than that connected in beginning of the feeder, especially when the feeder impedance is larger.
This relay is created by applying intentional time delay after crossing pick up value of the current. A definite time overcurrent relay can be adjusted to issue a trip output at definite amount of time after it picks up.
Related EEP's content with sponsored links. It helps you to shape up your technical skills in your everyday life as an electrical engineer. Leave a Comment Cancel Reply. Subscribe to Weekly Digest Get email alert whenever we publish new electrical guides and articles.October 11, 43 Comments. Filed under Uncategorized. About Jignesh. Parmar B. Tech Power System ControlB. E Electrical. Membership No:M He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India.
Since it is energy it is always consist of Power P which equal with current I and consist of t time. Whereas high over current setting is to limit short circuit withstand. Setting high over current setting shall be wise to distinguish between real short circuit and starting current. Hello sir, I am not clear with this explanation, can you explain with some example. But i have noticed that at some places SQ. Does HT cable selection is related with fault level and HT cable at 11 kv should not be used less than Sq.
For HT Cable one important criteria which need to be consider is Short circuit level. Normally 11KV S. C level is 20 to 25KA at it varies according to Electricity provider company. C falls in 17 to 20KA. For HT cable you have to consider S. C level of utility first than Current carry capacity of Cable. Please let me know the details of selection of Neutral grounding resistance.
Your suggestion please. Dear K. F is better to make it less or equal 1 ,it means always lagging. We are going to synchronize 30MW,11kv DG with this grid breaker. Power failure time, I wish to isolate grid feeder. Please advice. Sir, thank u for your notes on Normally inverse curve. By the same way plz give the formula for Extermly inverse curve.
You may assume any capacity of transformer installed in the outgoing feeder in above example.
Sir, I would like to known how relay can be wiried and implemented and settings and how its configured in relay panel. And i had a doubt, this realy implementation and configuration and setting are different from one another?????? Sir, I would like to know why there are some differences between the theoretical operating time and the experimental one?
Why is that lower injection current with larger error? Thank you! Respected Sir, please guide, the following values are given as above example, are these also to be calculated?You can also find here poker player profiles, tournament poker results, poker rules, poker strategy articles, poker magazines, poker tools and poker training resources.
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Inverse Time Over Current (TOC/IDMT) relay trip time calculator
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