Estimation of the primary current using the secondary current from a saturated CT

  • 4.34 MB
  • English
UMIST , Manchester
StatementS. Sanno ; supervised by P.A. Crossley..
ContributionsCrossley, P. A., Electrical Engineering and Electronics.
ID Numbers
Open LibraryOL21239883M

Estimation of primary current in saturated current transformer using flexible neural network March Transactions of the Institute of Measurement and Control 28(1)   This Video Demonstrates How to calculate the Primary current given the Secondary Current for a current transformer CT using the turns ratio.

The accuracy of CT‟s is defined by IEEE Cas the extent to which the current in the secondary circuit reproduces the current in the primary circuit in the proportion stated by the marked ratio, and represents the phase relationship of the primary current.

Under normal (steady state) operation the difference between primary current i 1 and secondary current i 2 can be calculated by the turns-ratio of the CT and the magnetizing current can be. Abstract: Current-transformer (CT) saturation causes severe distortion in the measured current waveform which may lead to maloperation of the protective devices.

This paper proposes a low-cost, power-electronic device to prevent the CT from saturation. The proposed compensator is inserted in series with the relay in the CT secondary circuit and acts as a controlled voltage source (CVS).Cited by: 8. Under ideal conditions, the secondary current developed by CT will be the primary current divided by the CT turns ratio.

However, the CT secondary current will not be a sine wave when the flux in the CT core reaches into the saturated region. One important factor affecting this is asymmetry in the primary current (i.e.

Download Estimation of the primary current using the secondary current from a saturated CT PDF

DC component). When current transformer gets saturated they no longer supply secondary current proportional to supplied primary current. Depending on the level of saturation the measured current on the secondary is much smaller than the value present in the prim.

For the secondary excitation voltage at a current of 20 times the rated secondary current of the CT (Ue = 20 × 5 × = V) as well as the core weight (W = kg) and the total magnetic losses (P = W/kg), σ is calculated by Eq.

(12): (12) σ = P U e 2 = × 2 = 7 × 10 − 4. The relay connected to the CT should operate for 60A of symmetrical primary current. CT internal resistance= Ω, lead resistance=Ω, relay burden=Ω.

Calculate the actual primary current need to trip the relay. Answer: Number of turns =50/5= Relay operates for 60/10=6A of CT secondary current. The example in Fig. 3 shows the primary current decreasing in magnitude every cycle. The point ofthis is to show that if primary current magnitude decrease, the CT is saturated for s less time.

The lower magnitude in the second cycle of 3 Fig. generates a weaker magnetic field, requiring less flux density to replicate the current correctly. The CT ratio is the ratio of primary current input to secondary current output at full load.

For example, a CT with a ratio of is rated for primary amps at full load and will produce 5 amps of secondary current when amps flow through the primary. If the primary current changes the secondary current output will change proportionally.

However, the CT secondary current will not be a sine wave when the flux in the CT core reaches into the saturated region. The factors affecting this are secondary burden, primary current magnitude, asymmetry in the primary current, remanent flux in the CT core, saturation voltage, fault inception angle and CT turns ratio [1].

N 2 = number of turns on the secondary, V 1 = primary voltage, V 2 = secondary voltage, I 1 = primary current, I 2 = secondary current.

Example: A 50 kVA single-phase transformer has a V primary, and a V secondary. Assuming an ideal transformer, determine (a) the primary and secondary full-load currents, (b) the transformer turns ratio. Figures 5a through 6b present a series of secondary currents superimposed on the ratio current.

The primary current ranges from to times the CT rating (10kA to 75kA in this case). All traces are rescaled to the peak of the ratio current for easy visualization (in this way all currents.

Details Estimation of the primary current using the secondary current from a saturated CT PDF

After CT saturation has been detected, the current samples and phasors in the latest unsaturated period are used to correct the saturated current samples. The proposed algorithm was tested using MATLAB/SIMULINK simulator and realized on a DSP Starter Kit to demonstrate its effectiveness and applicability.

of the primary and secondary current (Fig. The ratio of the secondary current over the true primary current for both components gives us an overview about the level of saturation.

The level of the saturation can be classified on the base of the ratio of the RMS secondary current values over the RMS true primary current magnitude [3].

Description Estimation of the primary current using the secondary current from a saturated CT EPUB

The. In this model, the conventional CT symbol is assumed to be an ideal CT where the rela-tionship between the primary (Ip) and secondary current (IST) is a function of the turns ratio only. The impedance across the secondary terminals is called excitation or magne-tizing impedance (Ze).

This is a nonlinear impedance and its magnitude depends on the. Provided the CT is not in saturation, the secondary voltage is the product of the connected burden impedance and the secondary current: [math]V_s=Z_sI_s\tag*{}[/math] If the CT is in saturation, the above equation can no longer be used because the.

Rated voltage of the primary circuit – General case. Specific case: If the CT is installed on a bushing or a cable providing insulation, the CT can be LV ring type. Primary service current (Ips) Knowledge about the primary service current will enable us to determine the rated primary current for the CT taking into account any eventual derating.

The bottom line is that the current waveform on the secondary of a saturated current transformer may be diverse depending on what components are present on the primary current and also on the burden wired to the secondary circuit of the current transformer.

Current transformer saturation leads to protection devices mis-operation as the measured. Lecture Estimation of System Frequency; Module Differential Protection of Bus, Transformer and Generator. Lecture Bus Protection; Lecture Transformer Protection; Lecture.

5 Using the C standard burden of 4 Ω and the actual CT burden of Ω: 4 Z Z Z STD Burden b = = = (3) With an X/R ratio of V S ≥ ()20+1 ⋅⋅ = (4) Consequently, for power plant auxiliary applications, current transformers used with the.

A current transformer (CT) is used to measure current in a shunt inductor connected on a kV network. The CT is rated A / 5 A, 5 VA. The primary winding which consists of a single turn passing through the CT toroidal core is connected in series with the shunt inductor rated Mvar, kV (kV/sqrt(3)), 1 kA rms.

Suppose one current transformer has rating /1 A and ISF is and another current transformer has same rating with ISF 2. That means, in first CT, the metering core would be saturated at × or A, whereas is second CT, core will be saturated at 2 × or A.

This characteristics are Current transformer burden, knee point voltage, saturation of current transformer. As the current transformer has two windings, in some cases it is confusing about the load of it. But the fact should be clear that- The current of primary circuit is the load of a current transformer.

CT or current transformer burden. a bar primary /5 ct has a secondary winding resistance and leakage reactance of (+j)ohm if the flux density has not be exceed tesla at 10 times the rated symmetrical current determined the maximum value of the resistive burden which can be connected, the core cross section is 30cm2.

Also, although the secondary current may fall to "practically" zero, there will always be some current due to the "air cored" flux of the primary bar linking the toroidal coil of the CT. Some CTs, often called Rogowski Coils, are entirely air cored and can avoid saturation problems, but need special integrating amplifiers.

With CT primary, being in series with supply voltage(in VT it is parallel to supply)the primary current is the load current and when secondary is open circuited, the primary AT will generate high voltage on secondary proportional to primary secondary is loaded, primarY AT will be same as secondary AT.

deliver the secondary current. The transformer draws an exciting current to keep the core excited [3]. Similarly, CT’s experience copper losses, core losses, eddy losses and leakage flux. So the secondary current of a CT is not a perfectly true replica of the primary current in magnitude and there may exist a small phase shift.

CT: current transformer. Overrating of a CT: selection of a CT whose primary In is greater than the n immediately greater than the load In. Matching, auxiliary or interposing CT: low voltage CTs installed at the secondary of the main CTs for correcting a ratio and/or the current phase shift.

SF: security factor. Nominal current of the motor * A* on the primary side side should be in the range of the setting of the protective devices at secondary side * 5 A *. For your motor / 5 A is probably good ratio of current transformer.

In addition, you need to see voltage level and the accuracy class of the current transformer.A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC).

It produces a current in its secondary which is proportional to the current in its primary. Current transformers, along with voltage or potential transformers, are instrument ment transformers scale the large values of voltage or current to small.

The standard current transformer secondary winding is rated at 5A as per ANSI standards. Other rated currents such as 1A exist elsewhere. The main purpose of a current transformer is to translate the primary current in a high voltage power system to a signal level that can be handled by delicate electromechanical or electronic devices.