BURDEN
The
term of burden is always raised on the instrumentation transformers, both current transformer and voltage transformer. Sometime, term of burden is
also equated with the term of load. Since the understanding of
burden are very important
and significant to an accuracy class of
current transformer and voltage transformer, we
try to present it in a
comprehensive manner to assist
practitioners in the field of medium voltage control to
have better understanding of the burden.
As started, we will explain the meaning of burden for current transformer.
As started, we will explain the meaning of burden for current transformer.
BURDEN DEFINITION
Definition
of burden base on IEC 60044-1 standard.
The impedance of the secondary circuit
in ohms and power-factor.
The burden is usually expressed as the
apparent power in voltamperes absorbed at a specified power-factor and at the
rated secondary current.
Thus, a burden
can be expressed in two ways, namely:
Firstly, as the total impedance of the secondary circuit in Ohms. This definition is commonly used in ANSI / IEEE standard.
Firstly, as the total impedance of the secondary circuit in Ohms. This definition is commonly used in ANSI / IEEE standard.
The
following table of burden base on ANSI/IEEE Standard.
Below are sample of Metering Current
transformer technical spec base on ANSI/IEEE standard.
0.3B0.2
0.3 is indicating
class accuracy of current transformer, with limit error between +/- 0.3% and B0.2 is indicating a burden, with impedance
value of 0.2 Ohm.
0.6B0.9
0.6 is indicating
class accuracy of current transformer, with limit error between +/- 0.6% and B0.9 is indicating a burden, with impedance
value of 0.9 Ohm.
Secondly, burden can be
expressed as form of apparent power VA at certain power factor in the rated
secondary current.
This definition commonly
used in IED60044-1 standard. In this standard, manufacture has to perform class
accuracy using burden at certain value with power factor 0.8 lagging as shown
of below statement:
For testing purposes when determining current
error and phase displacement, the burden shall have a power-factor of 0.8 inductive except that,
where the burden is less than 5 VA, a power factor of 1.0 is permissible.
Note:
Burden and accuracy class is
2 things are interrelated, so it is always defined simultaneously. The value of error ratio and phase
displacement will shift from the pre-defined value that
is used when the burden is larger or smaller
than a predetermined limit
burden.
As we know,
the definition of the secondary circuit is a circuit
which is connected to the secondary coil of the current
transformer. Secondary circuit may
include a cable, or measuring and protection
equipment.
If illustrated in graphic form, the understanding of burden is shown in the below figure.
If illustrated in graphic form, the understanding of burden is shown in the below figure.
Thus, burden of current transformer
are includes all components
connected to the secondary coil
of the current transformer such as meters or protective
equipment, connectors, cable, indicator lights, and so forth. In the
above example, the burden including the connecting cable impedance and measuring
or protection equipment.
Since the resistance of connecting cable between the current transformer’ secondary terminal and measuring equipment
or protective equipment greatly impact the performance
of a current
transformer, then some of the
following should be noted.
- When measuring or protective equipment is located far away from the secondary terminal of current transformer, The secondary current should be used lower value, such as 1 ampere. Using a current transformer with a 5 ampere output rating for measuring devices located far away from the secondary terminals, will lead to a bigger VA that is absorbed by the cable.
- To ensure accuracy in the range of values corresponding to the results of the manufacturer, the value of the burden should be in the range of 25% to 100% of rated burden (for Current Transformer with standard IEC60044-1) or in the value of rated burden(ANSI / IEEE C57. 13).
- Use of a larger or smaller burden than the burden identifier (rated burden), will lead to the increasing of error ratio (ratio error and phase shift).
- Use of burden that is not suitable, it will also result a shifted value of FS or ALF, which can cause damage to the measuring equipment or the protective current transformer will easily saturated.
Betway Casino – Welcome Bonus of 200 Free Spins
ReplyDeleteBetway is one 출장안마 of the best names when it comes to https://octcasino.com/ online poormansguidetocasinogambling casino jancasino in the world. Their games are kadangpintar varied, generous, and generous with