delabs Circuits

Showing posts with label Test-Measurement. Show all posts
Showing posts with label Test-Measurement. Show all posts

Wednesday, August 03, 2016

Winding Insulation Resistance Measurement

I am working in power plant. we have a problem on one of gas generator. the problem is that low winding insulation resistance of generator rotor. it read 800 k ohm where the other generator read greater than 10 M ohm. at full speed, there is no Kv measurement. same time no standing alarm from excitation system. all equipment are indicated okay.

My question is that is the relation between low isolation resistance of generator rotor and Kv measurement?

Mail from - IB SA Arabia

There is no relation between insulation resistance and any other parameter of you system. Insulation Resistance depends on age, physical damage on windings, humidity, contamination, wear and tear.
Let me know where you are doing the KV measurement. If you are measuring leakage voltage due to insulation breakdown, you have to fix it. The relationship of parameters does not matter. Small leakages can be tackled with grounding, don't compromise on safety and quality.

Dana Tekno Crossmeg Insulation Tester

Dana Tekno Crossmeg Insulation Tester

It is possible you may be touching one of the probes when you measure insulation, that may be the 800K, Even if one finger touches the probe, the circuit is closed via earth and a low 1M measurement can be seen.

The rotor the chassis all need to be grounded, and insulation resistance has to be measured after all power connections or electrical connections are removed. The electrical terminations unit should float for proper measurement, especially when you have doubts. Tell me about your progress.


I did not get a reply later, but i may not have understood the question well. The question also lacks details. In HV breakdown measurements KV is applied, but it has to be done after disconnecting all points. Beyond a limit, HV testing becomes destructive. Leakage Monitoring and Earth Leakage Breakers can be used. Motor/Generator Protection Units too. Even an imbalance in the current or Three phase problems.

It is best to use a Insulation Tester to apply little above Normal Voltage and see leakage, if this is a routine quality check. Better still, have a current sensor on the earth line and use a data logger to keep a tab on the leakage levels, temperature and voltage of all motors and generators. Even sound/vibration sensors will be an advantage. Before these electrical equipment fail many symptoms can be caught by data logging and limit windows. An electronic instrument or Trip Circuit will operate or alert after a fault occurs. Data logging and analysis will warn of a possible Motor or Generator performance degradation. Symptoms Indicate problems, prevention better than cure. Data Recording, Graphs and preemptive measures better than Breakdown Repairs in the Night. Drop in efficiency is an indicator for maintenace, This also prevents mishaps and power wastage.

It is true some insulation faults will show up on vibration and high humidity levels. These have to be simulated. In operation testing has to be done with sensors and recorders for leakage current etc. not insulation resistance.

Learn more about Insulation testing
- delabs

Wednesday, June 01, 2016

LM3914 meter for 25 V DC

"I wish to assemble a bargraph display to indicate approximately 25volts dc.How many LM3914 I should cascade? How to calculate resistor value which is grounded from the junction of Pin 6 & 7 (Rhi &Ref.out)? Assuming i need to cascade 3 LM3914s,what is the method to cascade these ics? The display need not be precise or very bright. I hope you can help me out."

Mains Voltage monitor using LM3914

"I shall be very grateful. Can we do it in such a way that the first LM3914 displays 1-10 v & second 11-20v & the third 21-30v?"

Thank you again - Mail from AD

Reply from delabs

Have a look at the TI application note which has many examples. Understanding this will help you make your own solution.

LM3914 - Dot/Bar Display Driver

20-Segment Meter with Mode Switch

20-Segment Meter with Mode Switch

Analog and 3-1/2 digital display

Cascading is required if you want more resolution. Example for measuring 20V, you want to show in 1V per LED steps. It can withstand +/- 35 Volts input upper limit.

The inbuilt reference is 1.2V use it as shown in the Typical Application. This also helps in setting the brightness of LED display. You may need to use external attenuators, buffers or precision  rectifiers to measure AC voltages or High Level DC voltages.

Friday, March 13, 2015

Mains Voltage Monitor

i need a circuit design to detect generator voltage and display with LED for certain value of voltage. for example red LED"s for voltage under 180 V, green LED for 180-220V and Yellow LED for voltage above 240 V. i would like be glad if you would like to help me design it!

mail from KB

I have some designs that may do that easily. Have a look at them. We could modify them to suit your needs.

First the 230V has to be brought down to say 2.3V with a transformer or attenuator. Then we have to measure it with LED bar graphs, choose color of LED as required. If the measurement unit is a sealed plastic box then it can be transformer less.

Look at these first. Mains Stabilizer Circuit, In DMM Circuits see ....analog and 3-1/2 digital display for +/- 199.9mV. in LM3914 you can light up a bar graph or a single LED to show the Level.

in Water Level Sensors see Fluid or Water Level Sensor using reed relays - circuit example

DPM based on ICL7107 see AC voltmeter digital, 7107, pdf After you looked at all the circuits, Tell me how i can help you.

DPM based on ICL7107


i have seen almost all the source you show me. i got more explanation and also more confusion...!
well, actually all i need is not too complicated but maybe its tricky for me. i got the idea about using voltage comparator via voltage divider, not using transformer like you said. it is more reliable and easier, isn"t? but again i got little bit trouble to design it!

is it easy for you anantha? i hope you will give me best solution for it! if you dont have mind i will wait for your design as comparison, but not in hurry! Ok, thank you for your kind attention!

mail from KB

I will make a circuit for you as soon as possible. Do you need just 3 LEDs or more. do you have experience in using 230V supply safely as it can give shock. give me more details if possible.


Again thank you very much for your attention on my question. actually it will be better to have 9 LEDS for 3 kinds. i have some experiences in installing 220/230 V but not expert, dont worry about that i will try as safe as possible.

i would like to install picohydro for my garden with power about 300 watt using induction generator. it will be expensive and not comparable to use complete controller as well. so i wondering to have voltage indication to estimate voltage condition, or even you have experiences with picohydro or minimum requirement for it (controlling, safety) like overvoltage protection, etc. again i will be glad for it....!
i will wait for your answers.

mail from KB

Can you please explain in brief what is picohydro and how induction generator is used. I have attached a circuit, It is not tested, It might do the job. You must have basic knowledge in building, testing and troubleshooting circuits.

After a study of the circuit you can tell me more clearly your needs.


Ok, induction machine can also used as generator if you at least:

1. Drive motor faster than synchronous speed (slip = negatif)
2. There is reactive power from outside (capacitor/Grid)
I think you know it! in my case i used 3 phase induction motor with 1 phase output only (C2C connection),its more reliable and much better than 3 phase output for small power! its easy to build! any way, thank you for your design...!i will try to study it before i build.

mail from KB

The circuits you asked for with some explanation has been published here.

Mains Voltage monitor using LM3914

Simple Mains Voltage monitor


Thursday, March 06, 2014

Electrometer, Gauss Meter and EMF Meter

Hey folks, I'm brand new here and to tinkering with electronics in general. I'm looking into building my own electroscope.

My question is: What's the difference between a static field and an EMF field? There seem to be detectors for both, so I wanted to know what the difference is, and what the relationship between the two is.

Question by BCM USA

delabs Answer

Static Field could be Electrical or Magnetic. Electric Charge as a static Field can be measured using Electrometer

Electrometer, Gauss Meter and EMF Meter

Simple Electrometer - A trivial JFET electrometer isn't a new idea, there are millions of designs for them out on the Internet, this is just yet another. This one is slightly unique in that it is a bridge configuration that makes it ultra-sensitive, much more so than a gold-leaf electroscope, but less than a vacuum tube or electrometer grade FET device.

Static Magnetic Field is measured using A magnetometer  also be called a gaussmeter. Gauss_meter

"Magnetometers are measurement instruments used for two general purposes: to measure the magnetization of a magnetic material like a ferromagnet, or to measure the strength and, in some cases, the direction of the magnetic field at a point in space."

EMF is the field of a Moving Magnet, an AC field. This Moving Magnet could be simulated by a Sine Wave in a Coil. Use a EMF Meter for this. EMF_meter

See some Instruments that are used here - AlphaLab Gauss Meter and EMF Detectors