［ Hydropower Generating Systems ］

Digital Type Static Excitation
Control System
Keywords

Hiroaki Fujimori

Digitization, Static excitation system, Hydropower station, RoHS application, AVR

Abstract

As a next-generation model to our conventional analog type static excitation
control system (Type: YNEX97S Series), we developed a digital type static excitation control system (Type: YNEX11SD). The major features of the newly developed
system are (1) multi-function, high performance, and compact design, (2) applicable up to a ﬁeld current of 912A, (3) the adoption of the Restriction of Hazardous
Substances (RoHS) directive- compliant parts, (4) improved operability with alarge-sized display, and (5) the adoption of self-diagnostic functions. We especially realized a very compact excitation control unit: W225 × H311 × D175mm.

1 Preface
Recently, the digital system has become thedominant trend in control equipment. Even for astatic excitation control system for a hydropower
plant, demand for digital control is increasing. We
have developed a digital control unit drawing on our
digital technology of a brushless type excitation
control system in which we have many records ofsupply. This paper introduces the features of thedigital type static excitation control system (Type:YNEX11SD).

2 Features
Fig. 1 shows a human interface part of the digital type static excitation control system and Table 1
shows a comparison with a conventional model.
The major features of this system are as follows:( 1) A multi-function, high performance, and compact design
Control functions of AVR primary and secondary circuits and gate phase control functions aredigitized and concentrated in a single unit. As aresult, we realized about a 10% size reduction(about 20% reduction of footprint space) comparedwith conventional model. For the excitation control
unit in particular, we realized a very compact size:
W225 × H311 × D175mm.
( 2 ) Adoption of the Restriction of Hazardous Substances (RoHS) directive-compliant parts
All parts used in the unit are RoHS direc-Fig. 1

Human Interface Part of Digital Type Static
Excitation Control System

We realized a very compact design while improving the operability
by using a large display.

tive-compliant.
( 3 ) Improved operability
Operational functions are sufﬁciently improved
thanks to the adoption of a large-sized display andsheet switches.
( 4 ) Redundancy of control power
We realized the redundancy of control power,both DC (110V) and AC (110V). The AC powersource is obtained from the secondary circuit of theexcitation transformer. For this reason, continuous
operation is possible even though the DC control
source is lost.
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Table 1 Comparison with the Conventional Model
By adopting the digital type, we increased such functions as thecommunication and secondary circuit regulation.
New type of staticexcitation unit
( YNEX11SD)

Conventional type ofstatic excitation unit( YNEX97S)Control method

DigitalAnalog

Voltage control

Control range:
80〜110%Control range:
80〜110%Control accuracy:
within ±0.5%

Control accuracy:
within ±0.5%

Control range:
80〜110%Control range:
80〜110%Control accuracy:
within ±0.5%

Control accuracy:
within ±0.5%

Field current
control

Voltage estabWith overshooting
lishment control reduction control(Overshootingreduction control) Smooth start or step
start system

Without overshooting
reduction control

AVR/MVR control Capable of changechangeover
over during operation

Changeover is notpossible duringoperation

Field overcurrent ○detection (51E )○−Excitation
undercurrent
detection (37E )×○ (Used for backup
protection of field loss)
relay “40”Sync pulse
monitoring forphase control○×Gate pulse
monitoring○○

Power supply
major fault
detection○ (Undervoltage/overcurrent/overvoltage)○ (Undervoltage/overcurrent)

Power supply
minor fault
detection

×○ (Either powersystem disconnection
detection)

41X dual contact ○ (Dual contact
monitoringmismatch monitoring
function)×○×

VT/CT fault
detection

Communication ○ ( TCP/UDP commu- ×
function
nication)
Fault trend
function○ (Dedicated toolrequired)

Secondary regu- Standard equipment
lation function

×

Available by optionalunit( 5 ) Fault trend function
When a dedicated tool unit connected, is afault trend analysis check at the time of a fault occurrence is possible.
( a ) Measuring signals: 8 points( b ) Status and fault signals: 32 points( c ) Sampling period: 10 ～ 100ms (variable)( d ) No. of sampling points: 1500 before fault, 500
after fault( 6 ) Simpliﬁed maintenanceExcept for the power supply board where electrolytic capacitors are accommodated, all other parts
do not require any periodic replacement. Since the30MEIDEN REVIEW Series No.167 2016 No.2

long-life type electrolytic capacitors are used, thelifetime of the power supply board has been extended
to ten years.
( 7 ) Productivity and application of component parts
We adopted the component parts which canprovide stable and long-term production.
( 8 ) Self-diagnostic functions
Functions of fault detection are available. This
works by checking the soundness among CPUs
through constant monitoring.
( 9 ) Minimizing performance changes and deterioration
Any component parts liable to face aging
detection (such as motor-powered setters and variable resistors) are not used. As a result, performance changes can be maintained at the minimumlevel. As such, inspection items are simpliﬁed andmaintenance costs are reduced.

3 Automatic Voltage Regulator (AVR)
Functions
Table 2 shows a list of AVR functions. The
major functions are described below.
( 1) AVR
Generator voltage is detected through a Voltage
Transformer (VT) in order to obtain deviation datafrom the voltage setter (90R). A ProportionalIntegral-Derivative (PID) controller is used for conversion to obtain phase control signals. By turning
the thyristor gate ON, the AVR output is controlled.
( 2 ) Automatic ﬁeld current control (AIFR)
Exciting current is detected through a CT todetermine the deviation from the ﬁeld current setter(70E). The obtained data are converted into phase
control signals by PID control. The AVR output iscontrolled by turning the thyristor gate ON.
( 3 ) Voltage buildup control( a ) Step start
When excitation control begins, the presetﬁeld current output is immediately generated. Whenthe detected generator voltage level attains thepreset value, the circuit is switched over to the AVR.
( b ) Smooth start
When excitation control starts, the ﬁeld current value is linearly increased within the presettime. When the detected generator voltage attains
the preset level, the circuit is switched over to theAVR. Thanks to this control, it is possible to reduce
generator voltage overshooting at the initial excitation of the generator.

Table 2 AVR Functions
In addition to the standard functions required for the AVR, thePSS is also available.
Item
AVR

Specifications
Voltage control range(90R)

80〜110%

Voltage control accuracy Within ±1%
Full-stroke time

60s

Field current control
range (70E )0〜110%I33

Field current control
accuracy

Within ±1%

Full-stroke time

60s

Voltage establishment control
function

Step start system(default)－Smooth start system

0〜100s

Cross current
compensation
function

Setting range

0〜10%

V/Hz function

Voltage droop system
Setup value (Drooping
point to be set up)

70〜100%FDefault 85%

AIFR

Field overcurrent Operating valuefunction (#51E )105〜130%
Default 110%

Field undercurrent function(#37E )

Operating value

Default 5%Power factor,
reactive power
control functions(APFR, AQR)
Q ＝ A ＋ BP
formulaItem A setting range−1.0〜1.0PU

Item B setting range−0.7〜0.7 cos φReactive power control
accuracy

Within ±2%

Power factor control
accuracy

Within ±2°

Reactive power
limiting function( VARL)Power System
Stabilizing (PSS)
function

OCL, OEL, UEL
OCL boundary setup

0〜100%

Lagging side setup

5 points Max.

Leading side setup

5 points Max.

3-lead, lag/4-lead, lag

Default: 3-lead, lag

VT, CT fault
Voltage and current
detection function difference detection
between phases

10% 10s

Gate pulse error
detection function

Pulse sequential order,
open phase detection

Continuous alarming
10 times
Continuous error 20times
Error: No pulse entry
for 200ms to besensed by #41XON

Dual contact
mismatch detection function

Contact inputs #41Xa, b 1s

( 4 ) Cross-current compensation function
In the case of parallel running with anothergenerator, reactive currents (cross-currents) ﬂow
between both generators due to a difference between
output voltages of these generators. This will resultin the consumption of extra-reactive power. The
cross-current compensation function of this system
can suppress generation of reactive currents (crosscurrents) by regulating the generator voltages according to the detected value of reactive power.
( 5 ) Functions of the Automatic reactive power
Regulator (AQR) and Automatic Power Factor
Regulator (APFR)
During the parallel running of generators, thereactive power or power factor of the generators canbe regulated to a constant level.
( 6 ) Power System Stabilizer (PSS) function
Fluctuations in power can be suppressed bydetecting such ﬂuctuations in order to adjust theexciting currents.
( 7 ) Communication function (LAN function)
One port of LAN interface is provided for use
as a maintenance port.

4 Postscript
Our digital type static excitation control unit
has been introduced.
Going forward, we will make efforts to increasefunctions and improve performance so that ourproducts can meet various requirements of our customers.
・All product and company names mentioned in this paper are
the trademarks and/or service marks of their respective owners.

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