فحص v.t ratio بواسطة جهاز c.t anyalzer

[بلال القضاة]

السلام عليكم
ارجو الافاده حول فحص V.T Ratio باستخدام جهاز C.T Analyazer وللعلم فحصت v.t ratio لمحول نسبة تحويله 33000/110 وكانت النتيجة للفاز الاول والثاني N=310 اما الفاز الثالث فكانت النسبه 303 مع العلم بان طريقة التوصيل كانت بنفس الطريقة لجميع الفازات السؤال ما مدى دقة جهاز c.t anaylazer عند استخدامه لفحص نسبة تحول محولات الجهد وهل نتيجة الفحص هذه مقبوله؟؟
السؤال الثاني كذلك بخصوص c.t analyzer ان تكرمتم بالاجابه .فحص class for C.t .هل يستطيع جهاز الفحص تحديد class for C.T ام فقط يتم ادخال class كمعلومات فقط وللعلم تم فحص محول تيار class 0.5 فعليا وتم ادخال class على جهاز 5p20) c.t analyzer) وكانت نتائج الفحص سليمه اي التقييم لجميع الفحوصات ok مع العلم بان class for C.T is 0.5 ؟؟

[OMICRON Academy]

regarding your questions.

1. VTRatio measurement is not accurate

For the VT Ratio test, the CTA Quick Card is used.
It is important to know that the OUTPUT and the input SEC are connected to the primary side of the VT and the input PRIM is connected to the secondary side of the VT. Please refer also to the picture below.
The input PRIM has a max. voltage range of 30V and the input SEC has a max. voltage range of 300V, therefore it is important to connect the input SEC to the side, where higher voltages can occur, which is the primary side of the VT.

CTAquestion_SayedSaad.png

In the VT Ratio test card you can select the voltage level (max. 40V) and the frequency to be applied. The turns ratio is then calculated as follows:

N = V_SEC / V_PRIM

Where as
N ... calculated turns ratio
V_SEC ... measured RMS voltage at input secondary (connected to the primary of the VT)
V_PRIM ... measured RMS voltage at input primary (connected to the secondary of the VT)

Voltage transformers can have a non-linear area, especially in the low voltage area. Therefore it might happen that you don't measure the turns ratio properly with the max. 40V. One trick would be to decrease the applied frequency. Let's say, apply 40V with a frequency of just 5Hz, this would be equivalent to about 400V at 50Hz.

I assume that this had been the problem, which you have faced.

Therefore for more precise results, the Votano 100 (new device dediacated for VT testing) had been developed, where it is possible to apply up to 4000V for the VT ratio measurement.

1. Assessment on a protection CT was “OK”, when the customer selected the metering class 0.5.

In this case we would need the measurement file (.xml) from the CTAnalyzer.
The customer should please provide one file, where he has measured with the metering class 0.5 and one file with the protection class 5P20.

• It would be advisable to use the 4.40 firmware, so to exclude any bugs, which may have been present in older CTA firmware’s. Firmware and instruction are attached.

The default measurement principle is the same for all current transformers.
The CTAnalyzer injects a current/voltage signal and measures the corresponding values back.
Depending on the selected CT data and the used standard, the measured values/parameters are calculated and compared to the limits given in the standard(s).

When the customer has now entered the wrong parameters and the tested CT still fulfils the wrong parameters according to the standard, then the CTAnalyzer will state that the assessment is okay.

Therefore would it be good to have the measurement files to check the parameters.