Question 1

What is the permissible overload percent for oil-immersed transformers?

Accepted Answer

The rated overloading of a transformer depends on the transformer's previous load, the corresponding windings or oil temperature at the beginning of the overloading. Examples of the permissible duration and the respective levels of the acceptable over loadings are shown below for oil immersed transformers. For example, if the transformer is loaded with 50% of its rated power continuously, then the transformer can be overloaded to 150% or to 120%, only the time will be the difference. Note: It should also be noted that the oil temperature is not a reliable measure for the winding temperature, since the time constant of the oil is 2 to 4 hours, while the time constant of the winding is 2 to 6 minutes. Therefore, the determination of the permissible duration of the overloading must be done very carefully, since there is a danger of the winding temperature exceeding the critical temperature of 105°C, without being visible for the oil temperature.

Question 2

What is the difference between XF and MX coils for ACB and can we use one instead of the other ?

Accepted Answer

The difference is indicated below :Closing release XF :The XF release remotely closes the circuit breaker if the spring mechanism is charged. Opening release MX: The MX release instantaneously opens the circuit breaker when energised. It locks the circuit breaker in OFF position if the order is maintained (except for MX “communicating” releases so we can't use the first instead of the second one .Please find the datasheets for the 2 coils for more info .

Question 3

What is the permissible overload percent for dry type transformers?

Accepted Answer

The rated overloading of a transformer depends on the transformer's previous load, the corresponding windings or oil temperature at the beginning of the overloading. Examples of the permissible duration and the respective levels of the acceptable over loadings are shown below for dry type transformers according to IEC 60076-12 and for transformer with thermal class 155°C (F). For example, if the transformer is loaded with 50% of its rated power continuously, then the transformer can be overloaded to 150% or to 120%, only the time will be the difference.

Question 4

CAD drawing for the following items: NW50H1HHF3P2E   NW50H1HHD3P2E

Accepted Answer

Please find attached the CAD drawings for 3P/4P versions of the NW50 Fixed/Drawout ACB.

Question 5

What is the difference between the TM-D and TM-G and MA tripping units for compact NSX MCCB Circuit Breakers

Accepted Answer

Circuit breakers equipped with thermal-magnetic trip units are used mainly in industrial and commercial electrical distribution applications: TM-D, for protection of cables on distribution systems supplied by transformers TM-G, with a low pick-up for generators (lower short-circuit currents than with transformers) and distribution systems with long cable lengths (fault currents limited by the impedance of the cable For Thermal protection (Ir) Thermal overload protection based on a bimetal strip providing an inverse time curve I2t, corresponding to a temperature rise limit. Above this limit, the deformation of the strip trips the circuit breaker operating mechanism. This protection operates according to: Ir that can be adjusted in amps from 0.7 to 1 times the rating of the trip unit (16 A to 250 A), corresponding to settings from 11 to 250 A for the range of trip units a non-adjustable time delay, defined to ensure protection of the cables. For Magnetic tripping (Im) Short-circuit protection with a fixed or adjustable pick-up Im that initiates instantaneous tripping if exceeded. TM-D: fixed pick-up, Im, for 16 to 160 A ratings and adjustable from 5 to 10 x In for 200 and 250 A ratings fixed pick-up for 16 to 63 A ratings For MA magnetic trip units In distribution applications, circuit breakers equipped with MA magnetic-only trip units are used for: short-circuit protection of secondary windings of LV/LV transformers with overload protection on the primary side. Magnetic protection (Im) Short-circuit protection with an adjustable pick-up Im that initiates instantaneous tripping if exceeded. Im = In x ... set in amps on an adjustment dial covering the range 6 to 14 x In for 2.5 to 100 A ratings or 9 to 14 In for 150 to 220 A ratings.

Question 6

I have an older SBO/EBO version, can I upgrade to latest EBO version?

Accepted Answer

System upgrades need to be performed in a prescribed sequence to ensure there is no loss of configuration or historical data. It is highly recommended that the Web Help procedures starting with the System Upgrade Workflows topic are followed carefully. See Functionality Upgrade section in WebHelp.WebHelp article can be found here:System upgrade overview * 3.3L is a Limited version intended for specific feature compatibility with some hardware and applications. Full support for thisversion will be shorter than normal and will expire upon the next fully supported release of EBO. Any SmartStruxure solution that is currently at 1.9 or higher can be upgraded directly to EBO V3.2. SBO V1.5, 1.6 and 1.7 can be upgraded firstly to 2.0, then on to 3.2. SBO V1.8 can upgraded firstly to V3.1, then on to V3.2. EcoStruxure Building Operation 3.2 or higher doesn't support the original AS’s often referred to as AS classic, Existing sites will require modernizing classic automation servers (SXWAUTSVR10001) with AS-P (SXWASPXXX10001), AS-P-SMK (SXWASPXXX1S001) or the AS-P-NL (SXWASPXXX10002) to run EcoStruxure Building Operation 3.2 (and later versions).It is important to read the current and ending version release Notes which can be found here: StruxureWare Building Operation v 1.5.0 Release NotesStruxureWare Building Operation v 1.6.0 Release NotesStruxureWare Building Operation v 1.7.0 Release NotesStruxureWare Building Operation v 1.8.0 Release NotesStruxureWare Building Operation v 1.9.1 Release NotesEcoStruxure Building Operation v 2.0.1 Release NotesEcoStruxure Building Operation v 3.0.1 Release NotesEcoStruxure Building Operation v 3.1.1 Release NotesEcoStruxure Building Operation v 3.2.1 Release Notes​​​​​​EcoStruxure Building Operation v 3.3.1L Release Notes​​​​​​EcoStruxure Building Operation v 4.0.1 Release Notes​​​​​​EcoStruxure Building Operation v 5.0.1 Release Notes​​​​​​EcoStruxure Building Operation v 6.0.1 Release Notes EcoStruxure Building Operation v 7.0.1 Release Notes

Question 7

What is the difference between type A & AC class RCCB ?

Accepted Answer

In Class A (Tripping is ensured for sinusoidal, alternating residual currents as well as for pulsed ,DC residual currents, whether they are quickly applied or slowly increased.Application: loads with electronics, rectifiers, and instruments.)Class AC Tripping is ensured for sinusoidal, alternating currents, whether they are quickly applied or slowly increased .

Question 8

What is meant by vector group for transformers and why is it important?

Accepted Answer

What is vector group for transformers?A vector group is the International Electrotechnical Commission (IEC) method of categorizing the high voltage (HV) windings and low voltage (LV) winding configurations of three-phase transformers.The vector group designation indicates the windings configurations and the difference in phase angle between them.Example: a wye HV winding and delta LV winding with a 30-degree lead is denoted as "Yd11".Common vector group presentations are tabulated below. Why is the vector group important to specify? As different combinations of winding connections will result in different phase angles between the voltages on the windings, transformers connected in parallel must have the same vector group because the mismatching of phase angles will result in circulating current and other system disturbances.

Question 9

What is meant by Symmetrical and Asymmetrical breaking currents?

Accepted Answer

issue:Customer wants to know the value of the symmetrical and asymmetrical breaking current of the circuit breaker and what do they mean.Environment:Circuit Breaker Resolution:- Symmetrical breaking current is the RMS value of AC component of short circuit current at the instant of separation of the contacts. It does not take into account the DC offset.- Asymmetrical breaking current is is the RMS value of the combined sum of the DC and AC components of the short circuit current at the instant of separation of the breaker contacts. This DC offset is of decaying nature which is dictated by the time constant of the system. As shown in the above picture the DC offset decays in a few cycles and is left only with the symmetrical component. Hence if a breaker has to close before the DC component decays, then the breaker’s breaking capacity is to be calculated for the asymmetrical current at the time of breaking.

Question 10

How to reset Zelio logic password?

Accepted Answer

The password can be reset by clearing the program inside the Zelio either byTransfering a new program to the ZelioOr Clearing the program that already exist by updating the firmwareKindly find the steps a) Clearing the program.b) Module / Update module firmware.c) Clear the Program Contained in the Smart Relay

Question 11

What is the selection criterion of Circuit Breakers for the Capacitor bank application.

Accepted Answer

The selection should be done after derating the Circuit Breaker taking into consideration voltage variation and capacitors tolerances that could increase nominal current up to 1.5In. The Derating factor of 1.5In Where In = Q/ ( Square root of 3 ) Un Q = Capacitor Power Un = Nominal Voltage Choose the Micrologic with delay time selection, so that the Circuit Breaker does not trip due to initial high inrush current. Also to be taken into account are the parameters like supply frequency, operating voltage & harmonics level of the power system for such application. Refer the attached sheet for further details for selection of Circuit Breaker for Capacitor duty application. Note: Use the phase barrier between the phases in Circuit Breaker to prevent flashover due to heavy inrush current.

Question 12

In a 3 phase system, why does the meter still show voltage reading on one of the phases even after breaking the phase circuit?

Accepted Answer

Issue:Testing phase loss on a meter doesn't result in a null voltage reading.Environmnet:EasyLogic Series Power MetersPowerLogic Series Power MetersResolution:The voltage seen is what we call "phantom voltage", its a known phenomenon with all high impedance power meters. These phantom voltages are normal artifacts of the design and should not pose any safety concerns to the end user.In some cases it'll probably disappear by power cycling the meter. Most power meters are not designed to monitor phase loss, as it'll always assume the presence of the 3 phases and the neutral, depending on your parameters setup. External devices are used to detect such occurrences, like phase control relays.

Question 13

Which RL(lead resistance from CT to relay) is to be used in Knee Voltage calculation if Current Transformers (CTs) used in High Impedance Restricted Earth Fault are at different distances from relay?

Accepted Answer

Issue:Having two different values for RL ( Lead resistance from the CT to the relay); RL from the phase CT to the relay and RL from the neutral point CT to the relayEnvironment:Protection Function ANSI 64refHigh impedance differentialSepam 80 Current Transformer requirementResolution:In any application where the high impedance differential is used, all the CTs must have the following:- the same ratio,- the same magnetizing curve (same minimum Vk),- the same maximum Rct (current Transformer secondary winding resistance),- if the relevant CTs are not at the same distance from the relay, take the maximum RL.Attached Cahier Technique no.194 for more information about high impedance calculation

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