123MB
Electrical
- Apr 25, 2008
- 265
Hi All,
I am trying to do an ad-lib dissemination of the functionality of devices like the Bender ISOMETER isoPV which are intended to perform insulation resistance measurement for energised electrical systems (i.e. PV plants).
I do not fully understand the theory of operation, but what I do understand is as follows:
1) The device is connected between the live lines and the bonding system
2) It applies a sawtooth waveform between each live line and the bonding system and observes the current returning through ground. The frequency of the sawtooth waveform is chosen so that it can be discerned from any other switching components present on the line (i.e. for VSDs or PV inverters).
3) It does a Fourier analysis or similar of the ground current waveform and uses this, together with the known frequency of the sawtooth waveform, to determine the AC and DC components
4) It uses the DC component to determine the effective resistance to the bonding system.
Does that sound correct? If so, let's move on to the next part of this discussion...
These devices have a 'maximum leakage capacitance' stated in their technical data, for example, 500 microfarad. I am trying to understand what relevance this has on the measurement - for example, if one exceeds the maximum - what happens? The documentation says that if the leakage capacitance is too high, the measurement will take longer - this makes sense as the charging and discharging of the capacitance will take more time - but what is the relevance of the maximum value?
Maybe it's just the limitation of the current source used for the measurement?
Thankyou.
I am trying to do an ad-lib dissemination of the functionality of devices like the Bender ISOMETER isoPV which are intended to perform insulation resistance measurement for energised electrical systems (i.e. PV plants).
I do not fully understand the theory of operation, but what I do understand is as follows:
1) The device is connected between the live lines and the bonding system
2) It applies a sawtooth waveform between each live line and the bonding system and observes the current returning through ground. The frequency of the sawtooth waveform is chosen so that it can be discerned from any other switching components present on the line (i.e. for VSDs or PV inverters).
3) It does a Fourier analysis or similar of the ground current waveform and uses this, together with the known frequency of the sawtooth waveform, to determine the AC and DC components
4) It uses the DC component to determine the effective resistance to the bonding system.
Does that sound correct? If so, let's move on to the next part of this discussion...
These devices have a 'maximum leakage capacitance' stated in their technical data, for example, 500 microfarad. I am trying to understand what relevance this has on the measurement - for example, if one exceeds the maximum - what happens? The documentation says that if the leakage capacitance is too high, the measurement will take longer - this makes sense as the charging and discharging of the capacitance will take more time - but what is the relevance of the maximum value?
Maybe it's just the limitation of the current source used for the measurement?
Thankyou.
