Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Current Transformer Connections - Resistors and Capacitors

Status
Not open for further replies.

FreshmanNewbie

Advanced Member level 1
Joined
May 10, 2020
Messages
405
Helped
0
Reputation
0
Reaction score
3
Trophy points
18
Activity points
4,031
I was just going through the purpose of the Current transformer and its working & using.

I found some schematics where I found a common pattern as below. It is a single-phase connection. LINE & NEUTRAL is the input of a single-phase supply.

The LINE CURRENT & NEUTRAL CURRENT connectors are connected to a Current transformer.

The outputs I2P/I2N & IP/IN go as inputs to an energy-metering IC.

enter image description here

enter image description here

Can someone tell me what are the purpose of the Resistors and capacitors in the above circuits and how the values are selected?

Also, I'm not able to understand the purpose of the LINE to VP connection.

I searched about the type of connections, but was unable to find it.

Any idea/guidance on this would be greatly helpful.
 

  1. In order to attenuate sampling errors from impulse noise, a low-pass filter with a cutoff frequency of 6.6 kHz (RC=1k*33nF) is employed. This filter ensures a phase shift of less than -1 degree at frequencies below 100 Hz, effectively filtering out current noise.
  2. To reduce Line to Vp, it is important to consider the creepage breakdown voltage, which can vary depending on factors such as dust, humidity, and conformal coating. Typically, resistors are rated for 250Vrms or higher voltages lasting less than 1 microsecond. However, nearby lightning strikes can induce common mode or differential impulses, generating high voltages (HV) that can lead to arc breakdown (< 8kV). To prevent such breakdown, it is recommended to use resistors with a higher voltage rating or employ protective measures such as gas tubes.
To enhance reliability, multiple resistors rated for 200~250Vrms are connected in series. This approach avoids fusing open if only a few resistors were used or creating a crater on the PCB the size of a dime when relying solely on a gas tube for protection. Previously, 8kV rated ceramic hybrid resistors with a zener bridge were commonly used in offline linear supplies for AMR (automated meter reading). However, the observed solution might differ from this standard approach. A well-designed layout incorporating an air gap and silicone sealant may have been employed to mitigate impulse safety testing failures caused by dust accumulation in the field.

I was just going through the purpose of the Current transformer and its working & using.

I found some schematics where I found a common pattern as below. It is a single-phase connection. LINE & NEUTRAL is the input of a single-phase supply.

The LINE CURRENT & NEUTRAL CURRENT connectors are connected to a Current transformer.

The outputs I2P/I2N & IP/IN go as inputs to an energy-metering IC.

enter image description here

enter image description here

Can someone tell me what are the purpose of the Resistors and capacitors in the above circuits and how the values are selected?

Also, I'm not able to understand the purpose of the LINE to VP connection.

I searched about the type of connections, but was unable to find it.

Any idea/guidance on this would be greatly helpful.
 
Last edited:

Hi,

* first link does not work for me
* Second link sadly isn't an internet page but a datasheet.

Klaus
 

If those "2.4E" resistors are meant to be 2.4 ohms then they
are likely the CT's "burden resistor".

The rest seems to be HF filtering and common-mode-zero.
Presumably the CT core & winding is the only thing "to the
left of J6 / J7" and isolates both hot and neutral, and all
"figuring" is referred to Earth (ground symbol).
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top