RFL 9300 RFL Electronics Inc.
August 9, 2001 4 - 1 (973) 334-3100
SECTION 4: SETTING GUIDELINES
4.1 INTRODUCTION
This section provides guidelines to help the user determine the parameter settings required to adapt the RFL
9300 to a specific application. For background and basic concepts, the user should first read sections 2 and 3 of
this manual. Instructions for entering settings can be found in Section 6 of this manual.
The RFL 9300 has over a hundred parameters that it uses during operation. A complete list of these parameters
can be seen in Tables 6-5 and 6-6. Some of the parameters are programmable, and others are read only. Ta-
bles 4-1 and 4-2 list all RFL 9300 parameters that are programmable. Space is provided in these tables for you
to record the settings you will need to make for your system.
4.2 PROGRAMMABLE PARAMETERS
4.2.1 PH BIAS - PHASE BIAS
Parameter #20 (PH BIAS) controls the phase bias. It can be set anywhere from 1.0 to 8.0 amperes,
in 0.5-amp steps.
The most sensitive phase bias setting (1.0 A) may not be suitable for all applications. The setting
should be selected on a case by case basis. Applications that require a higher setting are lines with
high charging current, lines with heavy tapped loads, and those with CT errors greater than allowed
for in (2) below. The 1.0 A minimum setting is based on an "error budget" that has three components:
1. A 0.25-amp "false differential current" caused by net line charging or a tapped load. (Net line
charging includes the effect of any line-connected shunt reactors).
2. 0.5 amperes for analog and digital resolution errors. This includes main CT errors at low cur-
rent, ACT error, A/D converter quantizing errors, and rounding errors in the local and remote
charges.
3. A 0.25-ampere safety factor.
Components 2 and 3 remain the same for many applications. Component 1 (false differential current)
remains 0.25 ampere for all untapped overhead lines up to about 50 miles in length, and all under-
ground cables up to about 5 miles in length. Tapped lines, 3-terminal lines, and longer lines will re-
quire a higher phase bias setting.
EXAMPLES
Tapped Line
A 20-mile overhead line has a tap that draws a maximum secondary load current of .2 am-
pere. A multi-phase fault on the low side of the transformer draws 2.0 ampere, based on
transformer impedance only. As described in Section 2, the phase bias is set
at three times
the let-through current, or 6.0 amperes. This setting accommodates full dc offset and in-
cludes Components 2 and 3 listed above.
Long Line
A 150-mile, overhead EHV line has a total charging current of 0.75 secondary amperes.
Since this exceeds the 0.25-ampere value of Component 1 above, the phase bias must be
set to the first level above minimum, or 1.5 amperes.
3-Terminal Line
Since an additional terminal with its own 0.5 ampere analog and digital resolution errors
is present in the system, a minimum phase bias setting of at least 1.5 amperes is rec-
ommended.
Very Long Line With Shunt Reactor Compensation
A 200-mile, 500-kV line has shunt reactors within the RFL 9300's zone of protection. These re-
actors prevent overvoltage under light-load conditions. The total capacitive current is 1.0 secon-
dary amperes. The shunt compensation is 50 percent, or 0.5 amperes. This results in a net line
charging current of 0.5 ampere, which is slightly above Component 1 of the error budget. There-
fore, a phase bias setting of 1.5 ampere is appropriate.
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