Frequently Asked Questions

Check for reverse installed current transformers. Also check for faulty current transformer as well as insuring that all current transformers used have the same secondary output current. Should all the aspects mentioned be satisfactory, check for loose connections, and effectiveness of any 3 phase closing isolating switches, contactors and circuit breakers and back-up fuses on the main phase lines to the motor. Taking readings of actual individual phase currents while the motor is running in order to establish the actual current variance between phases may also be necessary as a check. On those models permitting the user to set the unbalance trip thresholds you may find the setting somewhat tight. Consider any other applications in your plant that could have an impact on your power distribution network (for example the operation of an arc furnace).

The cold / hot thermal motor protection curves are always based on 6 times motor full load setting. Since, in the case mentioned above, your motor will be drawing this inrush current for considerably more than the permissible 15 seconds (cold start class) it is expected (and quite normal) that the motor protection relay will behave in the manner you have described. The solution to the problem is in the selection of the correct protection relay, which should allow for a larger motor thermal capacity. Select a motor protection relay that supports user selectable cold / hot thermal curves OR one that ignores the inrush current for a user selected time period. The latter may solve the practical onsite problems but is not a solution in the longer term since it exposes your motor to the possibility of a locked rotor condition during starting. In this case consider using another device such as a tachometer to insure the motor is actually turning and picking up speed. In some cases the motor selected for the application may need to be revised.

The cold / hot thermal motor protection curves are always based on 6 times motor full load setting. Since, in the case mentioned above, your motor will be drawing this inrush current for considerably more than the permissible 15 seconds (cold start class) it is expected (and quite normal) that the motor protection relay will behave in the manner you have described. The solution to the problem is in the selection of the correct protection relay, which should allow for a larger motor thermal capacity. Select a motor protection relay that supports user selectable cold / hot thermal curves OR one that ignores the inrush current for a user selected time period. The latter may solve the practical onsite problems but is not a solution in the longer term since it exposes your motor to the possibility of a locked rotor condition during starting. In this case consider using another device such as a tachometer to insure the motor is actually turning and picking up speed. In some cases the motor selected for the application may need to be revised.

Establish the current transformer ratio being used. For the purpose of illustration let us consider 3 examples.

Example 1
The motor full load is 82 Amp. The current transformers are 150:1. Simply divide your motor full load current by the primary side of your CT ratio selection and multiply by 100. In this case: 

82/150 X 100= 54.6 % or 55%.

Example 2
The motor full load is 177 Amp and the current transformer ratio is 200:5. Simply divide your motor full load current by the primary side of your CT ratio selection and multiply by 100. In this case:

177/200 X 100= 88.5 % or 89 %.

Example 3
The motor full load is 210 Amp and the current transformer ratio is 200:1. Simply divide your motor full load current by the primary side of your CT ratio selection and multiply by 100. In this case:

210/200 X 100= 105%.

Always install the current sensing transformers or the chassis mounted relays incorporating integral current transformers in the MAIN lines to the motor. Never on the delta loop of star delta configurations. There is no cost saving in so doing AND the relays perform with less likelihood of nuisance trips during the transition. 

All motor manufacturers can supply information on the insulating materials used in the construction of their motors (winding insulation), which is usually class F material insulation. In addition, they provide a means of determining the motor’s ability to dissipate heat. They provide this information by defining the safe cold stall time (at 40º) and safe hot stall time (at 120º) in seconds of the motor. In turn, these are referred by the protection industry as the cold thermal curve and the hot thermal curve respectively. Generally speaking there is a ratio of 3:1 between the cold and hot thermal curves.

Yes. This will roughly equate to 6 times motor full load current and introduces important design criteria for the protection relay. Consider the following:
How will the protection relay actually determine that the motor is running when we start the motor? After all it could manifest a locked rotor on start up?
How will the protection relay identify a running stall situation or JAM condition?
How will the protection relay distinguish a short circuit condition from a running stall condition?

Yes. The thermal condition of the protected motor is stored in a non-volatile memory area of the relay.

When installing a brand new relay it is not possible for the protection relay to know the thermal condition of the protected motor at the point and time of installation since it is being newly installed. For that reason some protection relays will start with pre-loaded thermal curves. Typically this means that if you have selected a cold thermal curve of say 30 seconds, on power up, the protection relay will only make available 10 seconds. If a start is not initiated the protection relay will see no current flowing to the motor and will slowly allocate more thermal capacity until the full 30 second curve is once again available.

It means that in the event of the power supply to the protection relay being removed, the main trip contact will de-energise and cause the main contactor holding coil to disengage and thus stop the motor.

The Company was established in 1978 and, at the time of writing, has delivered over 200,000 motor protection relays to the South African market alone. By virtue of the fact that the company continues to thrive in this very specific niche market despite competition from much larger international companies bears testimony to the quality of its products. Modern developments have accentuated a need for automation and control of plants. In this respect the company has and continues to embark on research and development so that its modern range of relays offers an all-encompassing solution to protection, control and automation of large plants. 

Very much so. We are very aware that modern trends are emphasised by the need for control, protection and even management of plants to go hand in hand when designing fully automated plants. For this reason we have designed our products to facilitate these requirements and have made it possible to accommodate a number of popular communications protocols such as Profibus DP, Modbus RTU and Canbus. We can also communicate via Device Net. Other communications protocols are being developed as ongoing projects. The main point being that our prospective customers must never feel locked in to any specific make of PLC usage. Present designs also permit and facilitate firmware software revisions to be down loaded on-site so that our customers can continuously benefit from any new software revisions that are made. In this way they are not burdened by having to purchase new relays in order to keep up with the latest protection features / benefits. 

We are pleased and very proud to say all products are designed and manufactured by NewElec.

Naturally. In fact we service and/or repair our products at a fixed price amounting to 30 % of their current list price irrespective of the age or nature of the fault(s). In doing so, we also renew the original product guarantee. See also our general terms and conditions of sale with specific reference to service and guarantee of our products.

This is both easy and difficult to answer:

There is no general industry out there to whom we have not supplied our motor protection relays. But in a more recent and modern context we can name Kumba Resources, Portnet, Columbus Stainless Steel, Umgeni Water, South Witbank Colliery, Douglas Colliery, Joy Mining Machinery, FFE Buffalo Minerals, Optimum Colliery and PFG Building Glass as good referral sources. We also design and supply motor protection relays for specific companies and under their own names if volumes are indicated.

Yes. To ensure quality management and manufacture of products we comply with ISO 9001. At the same time our products are designed to comply with European IEC specifications both in terms of protection as well as ISOLATION, IMPULSE WITHSTAND, ELECTROMAGNETIC INTERFERENCE and HIGH FREQUENCY DISTURBANCE requirements. More recently, all our PC boards are also conformance coated to assure the utmost resilience to chemical and corrosive atmospheres.

No. We prefer to have our products tested by Eskom who are also critical users of our products. Test certification from Eskom relating to any of our products is available to anyone requesting them. This does not mean we never intend to make use of the services of the SABS and is an issue open for discussion. However, in the interim, we consider the needs of our valued customers best served by the South African electricity supplier, as they are very demanding in their own selection of protection products.

Yes. However this has mostly been as a result of initiatives derived by our own customers who have included our products within OEM built equipment such as crane controllers or motor control centres. In the past we have had some success in introducing our products via a distributor in Zimbabwe. As a result of these efforts we are aware that our products are in use in China, Chile, Congo, Zambia, Mauritius, Tanzania and Botswana. We are nonetheless very interested in exporting our products to any country but primarily into Africa and would welcome all trade inquiries in this regard.

Yes. We provide training for your staff on any of our products. We prefer that these training sessions take place at our own factory. It is possible to accommodate up to 8 individuals at the same time. However, for client convenience, we also offer such training at the customer selected site and arranged times and date. Presently, we do not charge for training but it is envisaged that some charge will be levied for such training in the future to cover costs only. 

Indeed. There are many satisfied users of thermal bi-metallic relays out there. They certainly hold a place in the market. However, our contention is that those users who are satisfied with this protection form have not had motors exposed to arduous working conditions. Almost certainly they have had the pleasure of uninterrupted balanced 3 phase supplies and you will find their motors frequently running well below full load current.

When considering that a 1% sustained overload is responsible for a 2 degree Centigrade temperature rise in the motor, that factors such as unbalanced phase currents and fluctuations in the supply voltage add to the creation of undesirable heat it becomes understandable that one would seek better and more accurate protection. Thermal bi-metals are mass produced items exhibiting a degree of inaccuracy when purchased off the shelve. They become less accurate with time (being electromechanical devices) and should be changed every 3 years to retain some degree of accuracy. They permit and tolerate immediate or near immediate re-sets, which suggests that, their thermal characteristics are not linked to the actual motor heat-cooling rate. Moreover these inexpensive devices are slow to respond to phase loss while the motor is running leading to rapid insulation winding degradation.

There are other reasons for which we would be opposed to using these devices BUT the above outlines the main reasons.

We are quick to point out that there are inexpensive electronic motor protection relays on the market that provide similar protection to the thermal bi-metal type. Acquiring these do not address the main points which are: 
Accurate reliable overloading protection against both cyclic and sustained overloads with built-in thermal memory and capable of modelling two cooling rates. One for cyclic overloading and the other for when the motor is standing and no longer benefiting from the cooling fan .

Accurate and reliable phase unbalance and loss protection irrespective of motor loading with rapid tripping on phase loss.

Clear, latched fault diagnostic LEDs to assist maintenance personnel in establishing the nature of the fault .
NewElec motor protection products meet these BASIC and most important considerations throughout the entire range at all times.

The short answer is that there are horses for courses?. This is where the more experienced electrical / instrumentation engineer needs to take a closer look at the application he/she is dealing with. Let us take time to ponder the issues involved. The answers to the following questions will ultimately determine the model preference.

• What motor starting method will be used?
• Is the protection relay going to be mounted on a door OR on a chassis plate inside the MCC cubicle?
• What physical space is available?
• Would integrated current transformers be a pre-requisite?
• Would it be better for the relay to be calibrated in amp or percentage?
• How long will the acceleration process likely take?
• What application is being considered?
• Would there be a need to protect against earth leakage faults?
• Does the present circuit incorporate a back up circuit breaker and is there a shunt tripping facility available?
• Will we require a 4-20mA output loop for use as an analogue input into a PLC for monitoring motor load?
• Would we want a duplicate set of trip contacts to signal to a remote control room?
• Would we wish to incorporate short circuit protection?
• Would it be required to allow for field bus communications to a PLC?
• Would you prefer to match more exactly the thermal characteristics of the motor to the protection relay?
• Is the detection of load loss required?
• Is the protection relay required to do recordings of the motor loads while running?
• Will jam protection be necessary?
• Will thermistor inputs be needed?

Will digital inputs for control purposes be required? Will the plant be fully automated by means of one or more PLCs? 
These are some of the decision-making questions needing answers to make the wisest choice.

This problem is associated with the current transformers used during the installation which (if the relay is providing protection against earth fault and short circuit) should be class 5 P10. The problem can also manifest itself as a result of poor power factor correction and / or the use of a lot of VSDs. It all boils down to CT core saturation and harmonic content in the waveforms causing instability / spikes which is likely to occur when starting larger kW motors on DOL. You will need to do the following:

Ascertain there really is no earth fault present.

Start your motor while holding in the side mounted reset button.

On completion of the start sequence release the reset button.

If the protection relay trips on earth fault you will have to find the fault and clear it.

If no trip occurs, take a pair of side cutters and cut the solid wire link situated above the 47 Ohm stabilising resistor on the side of the relay. The problem will then be solved.

It is possible to alter the start timer seconds range by applying a multiplying factor of 4 to the scale. If this is done the timing scale will extend to 4 to 84 seconds from an initial 1 to 21 seconds. This can be achieved by opening the relay (4 rear base mounted screws must be removed) and sliding the relay slowly out of its casing. YOU NEED NOT SLIDE THE ENTIRE RELAY OUT OF ITS HOUSING! TWO THIRDS OF THE WAY IS SUFFICIENT. When you are able to see two bank sets of 8 dip switches exposed to your view, select dip switch bank PSS2 and move dip switch 1 to the off position. 

Yes. This is made possible by shifting a slide switch inside the relay from one position to the other. This can be achieved by opening the relay (4 rear base mounted screws must be removed) and sliding the relay slowly out of its casing. YOU NEED NOT SLIDE THE ENTIRE RELAY OUT OF ITS HOUSING! TWO THIRDS OF THE WAY IS SUFFICIENT. Look for a black slide switch on the top PC Board. The PC Board is marked 320 AD and is the board that includes the power transformers. Once you have found the slide switch move it from the 110 V to 220 V position or vice-versa.

This problem is associated with the current transformers used during the installation which (if the relay is providing protection against earth fault and short circuit) should be class 5 P10. The problem can also manifest itself as a result of poor power factor correction and / or the use of a lot of VSDs. It all boils down to CT core saturation and harmonic content in the waveforms causing instability / spikes which is likely to occur when starting larger kW motors on DOL. You will need to do the following:

Ascertain there really is no earth fault present.

Start your motor while holding in the side mounted reset button.

On completion of the start sequence release the reset button.

If the protection relay trips on earth fault you will have to find the fault and clear it.

If no trip occurs, take a pair of side cutters and cut the solid wire link situated above the 47 Ohm stabilising resistor on the side of the relay. The problem will then be solved.

This could be for any of the following individual or combination of reasons:

• The most frequent reason is that the 6 X I fl curve seconds is set differently on the respective relays
• The maximum load setting has not been set at the same level
• The motor r.m.s loading differs over a period of time
• One or more motors could have been stop/started consecutively prior to the observation
• One or more motors could be experiencing adverse unbalanced loading (low enough not to trip the motor on unbalance i.e less than 30%) but sufficiently so to reflect higher loading in the other phases and display a higher thermal usage content.

You are expected to set the safe cold stall time of the protected motor that is provided by the motor manufacturer. This could coincide with the acceleration time of the motor but need not necessarily be so. In essence the curve selection defines the acceptable thermal limits of the motor based on 6 times motor full load current. The setting should never be set above the safe cold stall time for the protected motor.

Resetting the relay after an overload trip will not be tolerated until the thermal lockout LED extinguishes. The delay is forced to ensure the motor has sufficient time to cool off. Our design will allow the relay to be reset just as soon as the motor looses approximately 33% of its heat build up OR just as soon as the LED bar graph illumination reduces to the reset indicator.

It provides a visual indication of how hard the motor is working. The green LEDs act very much like a delayed ammeter, reflecting the motor loading at the time of observation. When the orange and red LEDs begin to illuminate they indicate that the motor is working very hard, often being overloaded, BUT still within the thermal handling capability of the insulation material. When the entire LED bar graph is lit, a thermal trip has occurred OR is about to occur.