The problem usually encountered with this type of application relates to the high magnitude of the inrush current remaining present for almost up to 75 % of the acceleration period (D.O.L starting) which sometimes results in an overload trip if the protection is by means of a standard thermal bi-metal relay. In order to overcome this problem attempts are made to bi-pass the protection until such time as the motor has accelerated to speed.
The NewElec 320 to 327 series motor protection relays make provision for this condition while maintaining total protection of the given motor during the entire sequence.

This problem is usually experienced as a result of inadequate protection such as the thermal bi-metallic type and is further aggravated by phase supply losses from the incoming side. In our experience it is frequently the problems experienced by "thrifty" individuals who believe that modern electronic motor protection relays are too expensive.

We comment as follows:

• It is an established fact that thermal bi-metal relays cannot detect overloaded conditions much above 10 %.
  
• That such devices lose their accuracy with time due to their electro-mechanical wear.( They need to be replaced every 2 to 3 years if any token of accurate protection is required)
  
• That these devices do not accurately reflect the heat build up in a motor and that when they do trip, they do not reflect an accurate required cooling period before the motor may be safely re-started.
  
• Such devices will seldom trip on a phase loss condition unless the motor happens to be running close to full load.

All of NewElec`s product range will address the above difficulties BUT none more economically than the NewElec chassis mounted KB and LA range. Should flush door mounted products be preferable the NewElec NE range would be recommended.

There exists in many instances, where the loss of mechanical equipment can be directly associated with motor "instantaneous" overloads due to jamming conditions and the related effects of output torque suddenly increases. Consider for example a small 5,5 kW 4 pole 380 Volt motor driving a conveyor belt by means of a 160:1 gearbox.
The expected full load torque for such a motor would be in the magnitude of around 36 Nm at the motor output shaft. As a consequence of the speed reduction produced by the 160: 1 gearbox, the normal output torque at the gearbox output shaft would be in the order of 5,760 Nm.
Now consider a situation where a jam condition occurs on the conveyor side. The effects of such a condition will lead the motor in attempting to provide more power so as to overcome the jam condition. This in turn will result in a possible rise of up to 3 times the rated motor torque and a consequential rise to 17,280 Nm at the output end of the gearbox. If this is insufficient force to loosen the obstruction and no mechanical fractures occur, the motor will eventually be exposed to a locked rotor condition.
More often than not however, mechanical damage is experienced, the offending obstruction is forcefully cleared and the motor continues to run normally once again. Unfortunately, although no harm has happened to the motor there is an associated downtime cost in repairing the fractured mechanical part and associated spares.

The NewElec KC, NJ, NK, 320-327, MA and OLR 8 protection relays can all prevent such problems from occurring by disrupting the supply to the motor in such rapidity so as to prevent any mechanical loss due to impact torque conditions.
All of the above mentioned models provide this form of protection including other motor protection features. The OLR 8 is dedicated ONLY to this problem type.

By way of example, it is automatically assumed that if a medium is flowing out of a delivery pipe fitted to a pump that all must be well. In fact, the impellor of such a pump could be so worn by the abrasive nature of the medium being pumped that the pump’s efficiency is ridiculously lowered.

Again, a remote control station could, by way of a light indication, show that a particular motor is in operation and busy doing a certain task ( pumping a flammable gas out of a chamber for example). The fact that the said motor’s drive belt has broken or slipped off the pulley would not be noticed and could lead to a dangerous situation in a given process.

Pumps relying on the cooling effect of the medium which they are pumping are particularly susceptible to malfunction if the medium runs dry.

NewElec`s KA, KC, MA and the UCR 80 protection relays could alert plant supervisors of such fault conditions and disrupt the supply to such motors so that maintenance personnel might attend to the problems before other serious difficulties can arise.
All the relays mentioned above would address such problems and include a host of other protection features. However, the UCR 80 is designed ONLY for this specific reason.

It is sometimes required that a process controlling PLC triggers an event as soon as a certain motor load has been reached. By way of example, hot syrup is poured into a stainless steel vessel connected to a two speed mixer. The mixer begins to rotate while the syrup’s consistency hardens as it cools.
The resultant effect is additional load on the mixer motor. Just as soon as a certain load level is reached the PLC will activate the mixer motor’s second speed. This kind of load monitoring is frequently required in process control activities.
As such, NewElec has included a 4 to 20 mA output loop (representing the motor load) as a standard feature on its 320 to 327 as well as NJ and NK range of motor protection products.

Supervisory staff often wish they could, at the very least, know the status and fault conditions relating to given plant motors so that they might be in a position to advise maintenance personnel accordingly and / or be capable of safely re-setting the protection relay remotely.

The NewElec motor protection relay models NI; NK; 320-327 series and the MA range all have capability for this provision.

This additional protection feature is often desired by engineers in all types of plant environment. More often than not the earth leakage protection component is added into the MCC cubicles as a separate entity. In the past, the prevalence has been to select low sensitivity thresholds of 375 or even 500 mA with IDMT trip curves for any motors above 75 kW. The reason for this selection can be attributed to nuisance trips on start up associated with transient inrush waveform conditions (harmonics), particularly when starting DOL or on variable speed drive applications.
Another reason for using a totally separate earth leakage protection relay is to ensure that the latching trip contact is connected to the shunt mechanism of a backup ACB or OCB as the case might be. Certainly, this would be desirable so as to ensure that the main contactor IS NOT used to disrupt the supply to the motor on a potentially high developing energy fault condition. In this way assuring that the contactor contacts are not welded shut due to arcing.

NewElec is pleased to make available a number of earth leakage protection products which take into account the above considerations AND benefit all parties in terms of cost saving and MCC cubicle space requirements.
In the first instance, NewElec incorporates earth leakage protection with SAFE TRIP CO-ORDINATION on their NH, NJ, NK, and MA range of relays. The first three of these have fixed earth leakage trip threshold sensitivities of 250 mA with an associated 100 ms trip delay. Since we take care of harmonics in our motor protection design philosophy there is really no need to worry over nuisance trips when starting large motors OR concern yourselves about nuisance trips related to variable speed drive applications.
What’s more, the protection relays are sufficiently intelligent to co-ordinate the output trip contacts in accordance with the expected levels of fault current. The main trip contact will be energized to disrupt power to the main contactor ONLY when safe to do so. If not, the trip function will either be blocked to permit the back up protection to clear the fault OR channeled to an auxiliary trip contact in order to activate the shunt trip
mechanism on the backup ACB or OCB as the case might be. So there you have it, intelligent earth leakage protection combined inside the motor protection relay requiring no additional panel cut out which can either be door or chassis mounted! Furthermore, a core balance current transformer will in most cases already be integrated within the motor protection relay which translates into yet another cost saving component.
In the case of our MA relay we allow more control as regards to the earth leakage trip sensing thresholds and trip delay. This latter model allows you to set the detection thresholds anywhere between 250 to 1000 mA while we permit you to set the earth leakage trip delay from 100 to 1000 ms. However, control over which particular element of switchgear is used to interrupt the supply to the motor, will remain with the MA relay.

Should you still prefer to use a door mounted dedicated earth leakage protection relay we offer our GA range for your consideration. This is available in a number of earth leakage current level sensitivities while each model uniquely allows the user to select either an instantaneous or IDMT trip delay curve. These models will require a separate core balance CT available from NewElec in four ID sizes. These models, have been designed with high stability against harmonics as well as EMI and RFI interference.

In order to provide some safeguard for customers accustomed to plants being operated on a seasonal basis OR for motors associated with standby equipment NewElec offers the EC earth insulation lock out relay. This handy little protection relay will monitor the insulation level of the protected motor and cables feeding such motor while it is stationary. A change over contact connected in series with the start pushbutton will prevent the starting sequence if there is an insulation problem.

NewElec manufacture a range of compact protection relays ideally suited for inclusion within flameproof enclosures lending themselves particularly attractive for the protection of equipment in typical mining applications.
The 100 M series cater for protection against overloading of motors (sustained and cyclic overloading conditions), phase loss and unbalanced load conditions as well as short circuit protection with user selectable short circuit detection thresholds.
The MA range of relays with its associated parts will permit up to 8 different preset parameters to be altered to meet specific motor specification setting parameters by means of a couple of key strokes and can provide LED fault indications for all fault conditions both on the relay face and remotely by means of an optional extra RDU. The protection features offered by this range are almost unlimited and very comprehensive.

The NewElec MA range relays are designed to afford total and complete flexibility to prospective users. These relays are ideal both for stand alone applications or for connecting to a SCADA system via a popular communications protocol. Apart from a fully comprehensive number of fundamental protection features the user will benefit from all the extra values packed into this product.

Flexibility:

• Current ranges 0,5 to 250 Amp split over 5 current ranges
  
• Current range can be extended by use of interposing CTs
  
• Built in current transformers as well as core balance CT
  
• Two types of Remote Display Units available
  
• May be programmed via the BUS, by means of a laptop OR by one of the RDUs mentioned above
  
• Separate communications module aimed at meeting your own protocol requirements

Control:

• 4 output changeover contacts
  
• 5 digital inputs
  
• Relays accommodate a field voltage of 12 to 220 Volt a.c OR d.c
  
• Built in type 2 co-ordination
  
• Built in solid state timers linked to digital input and output contacts
  
• Three independent thermistor input circuits
  
• Fail or non failsafe relay configuration
  
• Standalone software will allow relay to be used for recording all 3 phases RMS loads, line voltage and motor thermal capacity for later analysis by means of a Microsoft Excel spread sheet

Economy:

• Pay only for the parts you require
  
• Free software
  
• Price uniformity throughout the Amp range
  
• Physical size uniformity throughout the range
  
• Completely reliable built-in earth leakage protection and thermistor input circuits
  
• Included recording facility with built-in real time clock
  
• Three years guarantee

The following NewElec relays will permit user selectable thermal curves based on the safe cold stall time of the protected motor. The protection relays, once given this data will automatically allocate a safe hot stall thermal curve calculated at 33 % of the cold curve selection.
This facility will allow the given motor to run continuously at its full rating without nuisance trips. The relays that can accommodate this setting are the NE, NH, NJ, NK and MA relays. All other relays in the NewElec range have fixed factory selected cold thermal curves of 15 seconds translating to 5 second hot curves.

When it becomes necessary to provide good protection to motors designed for specific "S" ratings, complete starts per hour and specified Cyclic Duration Factors NewElec can again deliver. This is achieved with the design of the 330 M series motor protection relay which takes account of the above technical requirements and thermal considerations.

NewElec has 3 types of relays in the K Series which have been developed for exactly this purpose. They are very compact and designed for chassis mounting. Up to 25 Amp no additional current transformers are needed. Refer to the NewElec KA, KB or KC ranges.

One could also have a look at the more sophisticated MA range relay for the larger kW rated pumps.