Author: ABBdriveX

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AQ: Lighting control panel to distribution board

There are a couple of construction differences which may be present, depending on the style of “lighting control panel”.

First, a distribution board typically has poly-phase branch breakers with the intention of feeding either other sub-panels or large loads — such as a motor with a motor controller.

A lighting control panel will have mostly single-pole breakers with phase-to-neutral branch circuits feeding lighting circuitry. There is the added possibility of having either ‘smart’ breakers or integral contactors included on the branch circuits to allow for a control means for area lighting beyond local control of an individual fixture/small group of fixtures, such as an office or conference room.

In general
1. The final branch circuits to be identified and rating load to be estimated.
2. Adequate utilization/diversity Factor to be applied if applicable (depends on the application).
3. To ensure the load balance over the 3 Phase as possible.
4. For Fluorescent light fixtures arrangement of the said fixtures with respect (RYB phases) is necessary to mitigate rendering/glaring and frequency affect.
5. Then size of cable from DB to LCP can be determined/sized, rating of the protective devices can be selected and type of CB(s) subject to type of lighting fixtures.
6. Verification of Voltage drop within the prescribed limit, otherwise select the next standard cable size.

A distribution board typically has poly-phase branch breakers with the intention of feeding either other sub-panels or large loads and lighting control panel (is also one type of distribution panel) will have mostly single-pole breakers with phase-to-neutral branch circuits feeding lighting circuitry.

AQ: Why BLDC motors are noiseless compare to Induction motor?

If referring to the acoustic noise generated at or around the PWM frequency of the PWM frequency. There are more laminations in an induction machine. This may account for some of the difference.

I also don’t know what the relative power difference is between the BLDC and the induction machine. If it’s about a 5Hp BLDC and a 100Hp induction machine, then you can bet that the PWM frequency of the BLDC is likely above the audible range and the PWM frequency of the induction inverter is well within the audible range.

These are just a few reasons that you may find subtle differences between the two. There are many factors and more information is needed to really help understand your specific situation.
I also believe there are simply sophomoric and unprofessional answers. My statement is based on the general rule that there is greater surface area between laminations of squirrel cage induction machine then there are in BLDC machines. Of course, if you want to state that you have a thin lamination on a long stack length design for a BLDC then there may be an argument that such a motor design when compared to a typical induction machine of the same power has a similar surface-to-surface lamination area. It is these laminations moving due to eddy currents at the PWM frequency that causes the audible noise.

BLDC can come with very small inductance which requires a higher PWM frequency, if you compare both them with controller that may cause different.
If you build 2 motor using exact mechanical shapes and electrical parameter they should be very close. You can build 2 induction machines from 2 different vendors to same electrical spec and they will not sound the same.

AQ: Torque ripple information from low resolution speed signal

Q:
I am trying to develop a controller for switched reluctance motor which minimizes torque ripple. My design is acquiring torque ripple information from speed signal. In simulation a high pass filter for speed gives me good ripple information. But in experiments I am using a 500 PPR optical absolute encoder to get the position and then calculate the speed using microcontroller (dspace) capture module. But the filtered speed signal does not provide much ripple information. Can you suggest any method to extract ripple information from low resolution speed signal.

A:
1. In simulation, do you consider motor inertia? Inertia filters out torque ripple’s impact on speed, resulting in a smooth speed signal. 2. Generally speaking, a low resolution position sensor produces speed signal of more noise, especially at low speed. I would expect more noise out of your high pass filter.

An encoder generally does not specify an accuracy for the A to A! channel or B to B! channel or it is so broad a spec that it is useless. If you have the ability to trigger a clock on A and B to determine the period between A and B channels the difference between successive reads will give you a good indication of your ripple.

In some cases of motor – encoder installations the mechanical alignment of the encoder to the exact center of motor shaft can cause misalignment noise to occur in the resolved speed signal. In theory the ripple signal could provide useful information however in practice there are too many other influences. Even the shaftless encoder mounting has some of these difficulties.

AQ: Bushing insulation testing

In bushing insulation test there are three major current elements which any of those could affect the test result. These current elements are Capacitive current

AQ: Overcurrent protection of generators

Overcurrent protection uses as back-up protection for protection generators from faults between two windings of stator (two phases of stator). Setting of overcurrent protection depends from two settings: current setting of relay protection and time setting of relay protection.

Current setting of relay protection represents minimal value of current under which relay protection will send signal to breaker to act and this value is higher from value of rated current in generator (higher from maximum allowed value of current in generator).

Time setting of relay protection represents time after that relay need to send signal to breaker to break fault. Of course, when we talk about time setting of relay protection, we need to have on mind time delay. Time delay represents time during other protections need to act before overcurrent protection acts in case where is overcurrent back-up protection for protection of generator.

Then there is voltage restrained time overcurrent protection (ANSI 51V) which is commonly applied on generators. The pickup setting of these relays reduces (becomes more sensitive) when the applied voltage reduces. It is supposed to aid in sensing faults that are electrically close to the generator terminals as there is insufficient fault impedance to maintain the voltage at the generator. It is especially useful in tripping out faults that have persisted long enough for the generator fault decrement curve to get to the portion where the synchronous reactance is the characteristic impedance. When this happens the fault current will be at the same levels as normal load currents and increased sensitivity is needed.

AQ: What is the best laptop for field work?

Dell D630 – it is the best laptop for field use I have used. And for some applications standard RS232 port is a must. We have Freja 300 test set which totally refuses to communicate with PC via widely available cheap USB-to-serial adapters. The only usable adapter I have found is semi-industrial type, costing about 50 Euro. Not that a price is so much concern, but it is not very convenient to deal with additional boxes, power supply units for them, etc. when commissioning at field.

But I do not expect you will have problems connecting Omicron via converters. We have been used CPC256 via various USB-RS232 converters without serious problems.
For communication with relay protections from Siemens and AREVA never had problems too. Cannot remember how it was with older ABB relays (last case we used them was 4 years ago), but newer ABB series are all with Ethernet communications.

So my advice will be – by special laptop for field work, not mix it with that for everyday office use. Load it with the minimal necessary software – MS Word, Excel, Adobe Reader, Omicron’s Test Universe and software for relays which will test.
For all these needs most older type laptops (4-5 years older) would be sufficient and you can buy for 200-300 Euro solid business class laptop. And also very important: look for non-glossy displays only!

AQ: How to select the right cable?

Before you select kind of cable for your consumer, you need to calculate expected operating current of cable which depends from rated power of your consumer. After that, before you select kind of cable for your consumer, you need to check size of cable which needs to satisfy next conditions:

1. you need to check cable if it satisfied limits in normal conditions without consequences in aspect of warming (normal work),

2. you need to check cable if he satisfied limits in abnormal conditions without consequences in aspect of warming (short circuit).

1. when you want to check cable if he satisfied limits in normal conditions, you need to choose installation place (trench, concrete channel etc.), you need to know heat resistance of land, you need to know appropriate temperature of land and you need to calculate number of cables in installation place.

Icalculate=number of cables*k1*k2*k3*k4*Irated cable>Irated (consumer)
k1 depends from installation place,
k2 depends from heat resistance of land,
k3 depends from appropriate temperature of land,
k4 depends from number of cables

2. when you want to check cable if he satisfied limits in abnormal conditions, you need to calculate expected current of short circuit and heat impulse in the place of installation.

If your cable satisfied these requirements, then you made the right choice.

AQ: Difference between DCS and RTU

DCS distributed control system: you can control the system within a certain given facility from different locations, either control room or other places, and you should keep in mind this facility could be a in several locations but yet, hard-wired interconnected. while
RTU (remote Terminal Unit): you can control the system remotely through internet or a secure satellite connection which in not recommended for sensitive operations/process but it is ok for stand alone and not crucial systems. and more.

DCS as part of SAS (Substation Automation System) is based on local control of relays, meters and switchgear and automation as per required logic and programs that could be hardwired for serial protocols (like DNP 3.0) or through fiber optic when UCA 2.0 or IEC 61850 protocols are used.
For RTU, it’s just interface between substations’ I/O signals and dispatching center (SCADA) through communication links and specific protocols (such as IEC 101,104, Indactic, DNP 3.0, etc.). In other words, RTU has no controlling role by itself, but DCS as part of SAS has all programmed control logic within substations and without even connecting to dispatching center.

For Electrical Network Distribution, a System is required for controlling, Load dispatch as well as monitoring. Therefore Distribution Management System (DMS) or DCS to be adopted as an integrated System. They are simply like SCADA. Composed from Hardware, software, interfacing means & communication media / protocol as indicated above.
RTU (remote Terminal Unit) include Processor and all the required interfacing facilities as well as I/O(s) Modules.

The brief description of such system may be as follows:
The Substation prescribed Signals (MV switchgears, Transformer, Substation Auxiliary Equipment, etc.) to be hardwired to a marshaling box to Interface Cubicle where RTU located, RTU to be patched to the interface plate. Via the selected media “say FOC” the signals will be transferred to the DMC/DCS Control Centre. Accordingly, the real time status of the NW can be monitored and controlling can be achieved from remote.

The aforesaid Signals to be listed and sorted as per the required application to facilitate system configuration, integration and programming (unique address, function, type, is it required for control, monitor or both, which is digital & which is analogue, etc.).

AQ: Flashover in busbars

As for XLPE cable testing, if XLPE is used for insulation in the switchgear, the cross linking will be treed by HV DC and permanently destroyed. For this reason, HV DC is no longer used for XLPE cable testing. The switchgear should have a power frequency withstand test only and not HV DC. Refer to the relevant switchgear standard for the applied rms voltage. Any XLPE insulation will need to be replaced as it is most likely has been damaged by treeing of the cross linkages in the insulation. A maximum of say 2.5 kV DC is allowed for IR and PI only.

Humidity plays important part in flashover. We faced a problem of flashovers in Air insulated 11kV Switchgear busbar compartments in rainy seasons. Any sharp edge will ionize the surrounding air, which becomes conductive to high voltage discharge. Moisture will hasten the process of discharge. During HV test also this aspect should be kept in mind.

And make sure the following:
Clean all the supporting bus insulators and spouts with CRC spray.
Ensure the earth bus continuity and its connection with the earth grid.
all PTs are taken out.
all CT ckt output shorted at the panel.
All LAs are disconnected
Conduct a general cleaning of busbars through CRC-sprays.
Megger the bus bar with 5KV between phases, and between phase to earth for 1 mints before HV test.
Ensure the earth bus continuity and its connection with the earth grid.
Use AC high voltage test preferably
Connect HV test kit body ground to the SWGR body ground.
Apply 80% of the power frequency voltage applied at the FAT test.
If you are doing with AC hv kit then this may be a larger unit and leakage current is exceeding and tripping.
Try for smaller sections of busbars/increase the leakage current if options are available.
Rate of rise of voltage should be in steps of 2KV/s and gradual.
Check tripping function of the test kit.
Apply voltage betweenL1-(L2+L3)=G-1mints
apply voltage in the same way between other phases also.
If it withstands ok alternately you have to go for individual inspection of the insulators/spouts.

AQ: What is ANSYS software?

This is a finite element analysis tool for various applications.
In power we get the voltage (stress) distribution in equipment like cables, bends in cables etc including stator winding of generators.

Once you go deep into it the applications become more apparent.  In mechanical engineering using FEM you can identify the stresses in each member of the structure and so on.

I believe ANSYS, Abacus, Nashtran etcare extensively used for detailed analysis of stresses including electrical stresses. Some of the above offer introductory courses on line.
One needs extensive and considerable insight into partial differential equations and advanced mathematics.