1 introduction
The synchronous motor by the power factor and the output
torque which its may move to the electrical network voltage undulation
is insensitive and so on the good performance characteristic to
monopolize the chela head in the high efficiency electricity
transmission domain, is the actuation large-scale air blower, the
water pump, the compressor first choice type. But the
large-scale synchronous motor starting is a quite complex question.
If starts with the reduced pressure, not only needs the very big
transformer, the electrical machinery structure is relatively complex,
also the starting has a bigger impact to the electrical network.
But uses the load 换相 synchronous motor the principle,
carries on the frequency conversion to the large-scale synchronous
motor to start, is the quite ideal method. This article three
agglutinates the host platoon air blower firing set take the Baoshan
Steel Corporation as an example, introduced the synchronous motor
frequency conversion starts principle, process as well as typical
breakdown and processing method.
2 firing sets basic composition and main parameter
The Baoshan Steel Corporation three issues agglutinated
in 1998 complete go into production, two hosts exhausts air blower
electric installation provided by Rolls-Royce Corporation.
2.1 firing sets characteristic
(1) does not have the jigger equipment,
true realization static starting;
(2) uses not brushes the excitation, maintains the
overhaul to be convenient;
(3) the numerical control system, the debugging was
convenient, enhanced the system reliability;
(4) the electric motor in the in-step condition
incorporation, to the motor, the electrical network impact is small.
2.2 main circuits structures
The main return route by falls presses the transformer,
three-phase all controls the bridge levelling circuit, the direct
current reactor, the crystal thyratron inversion, rises to press the
transformer and the synchronous motor is composed. Rectifier
control system for speed, electric current negative feedback double
closed-loop system; The inversion control system (OPE) and is
indirect -like (OPS) by the photoelectricity encoder the rotor
position sensor, uses in to throw the net to control 整步 the
trimming and the synchronized incorporation. System basic
constitution like chart 1 shows.
2.3 hosts return routes partial main equipment
parameter
Main return route partial main equipment parameter like
table 1 shows.
Attempts the 17800kW synchronous machine firing set
principle
Direct current reactor (DC-L) the function is
脉动?limits rectified output direct current under the certain
value, guaranteed the inversion work is stable. Considered the
crystal thyratron the breakdown voltage and the nominal current, the
system used has fallen presses the transformer, rises to press the
transformer. Because the variable current return route voltage
rank reduces, caused the rectification, to invert each 桥臂 has only
used a crystal thyratron.
3 startings processes
Sends out the starting from the starting instruction to
finish the synchronized incorporation, experienced has risen the
pressure to change the bypass - to put through the cut, "forced (off
and on) - the nature 换相" the cut, 整步 process and so on
trimming and synchronized incorporation, during had 3 times of
electric currents limits value cut.
After sends out the starting instruction, first invests the
excitation, then closes the firing set the input, the power take-off
valve, causes its investment movement, starts to start. Table in
2 demonstrations startings acceleration process, control mode and main
condition change.
Table in 2 startings acceleration process, control
mode and main condition change
Because the transformer is lower in the low frequency
effectiveness for a period of time rate, is insufficient to drive the
electric motor, the synchronous motor from when static starts the
starting, rises to press the transformer to be at the bypass
condition, until the rated speed 8% (4Hz), separates the by-pass
switch, puts through rises to press the transformer. When the
rotational speed promotes to 10% (5Hz), the electric current
restriction from 20% cuts to 50%. This period is uses forces to
trade the physiognomy, blocks the flow when 延迟?alpha advances
the rectification side 135°, simultaneously leads passes the after
flow crystal thyratron, thus as for does not affect inversion blocking
the flow because of the reactor energy liberation, fast shuts off the
main return route to block the flow, then when reduces alpha angle,
the input current starts the increase, reactor beginnings and ends
polar change, after flow crystal thyratron V0 automatic cutout.
After the host loop current falls to zero, after time release
rectifier and inversion crystal thyratron. Trades in the force
flows the stage, mainly examines the rotor position through the
encoder, thus triggers the corresponding crystal thyratron, causes the
inversion crystal thyratron lead angle is zero, enhances the start
torque.
When the electrical machinery accelerates to the rated speed 10%
to 14% (5Hz to 7Hz), 逆变?flows the way from to force to trade
the class to cut the counter electromotive force nature 换相, has
completed 换相 the way transformation. Namely through the
indirect examination synchronous motor stator winding induced
electromotive force indirect computation rotor position, may like this
the higher control precision.
Synchronous motor when low speed section movement, inverts the
bridge crystal thyratron to continue to lead passes the time quite to
be long, easy heat. When air blower low speed the load is
lighter, direct current limit value hypothesis in crystal thyratron
nominal current 20%. Waits the rotational speed to rise to 10%
litre presses when the transformer is at puts through the condition,
the electric current limit cuts to 50%, when the rotational speed
promotes to 17% after, cuts the electric current limit value in the
fixed magnitude of current, while this, in order to enhance the system
the efficiency and the mean moment, excitation way by exciting current
maintenance constant, changes the magnetic flux maintenance to be
constant. When the synchronous motor accelerates to rated speed
95%, the system enters 整步 the fine control stage. The
installment sends out from the starting instruction starts automatic
整步 trimming lasted approximately 90s.
After enters 整步 the fine control stage, the lock-on relay
basis electrical network voltage and in the synchronous motor terminal
voltage two frequencies bad values (Delta f), produces a rotational
speed trimming signal, automatically adjusts the DC voltage height
which the rectifier outputs, makes the trimming to the synchronous
motor rotational speed, causes two 频率?reduces to the target
value in. At the same time, the exciting current also by the
lock-on relay control, causes the synchronous motor terminal voltage
and the electrical network voltage peak-to-peak value difference
achieves the target value.
Through to the synchronous motor terminal voltage peak-to-peak
value, the frequency trimming, causes the synchronous motor stator
terminal voltage and difference of value the electrical network
voltage achieves time the following target: Delta f<1/4Hz, Delta
U<2% UN, Delta S gamma ?0 (Delta S gamma for 相位?, the
synchronized incorporation condition namely considers the
establishment. The system blockade rectifier and the inversion
completely trigger pulse, the output current drops zero. At the
same time, the electric motor merges the electrical network,
afterwards firing set power source side and the load side switch
minute breaks, conclusion starting process. 整步 trimming
stage lasted approximately 20s to 40s.
4 breakdowns phenomena and primitive treating
processes
4.1 incorporations overtimes breakdown
(1) breakdown phenomenon
The incorporation overtime is debugs the stage, and goes
into production a breakdown which the initial period comparatively
often appears. The main phenomenon is, after the rotational
speed approaches 1000r/min, cannot incorporate causes the starting
overtime defeat; In 整步 the stage exciting current is 85A to
130A between, obviously is bigger than the acceleration period 70A to
75A between.
(2) fault analysis
May know according to the synchronous motor rotational
speed formula:
In the formula: N electrical machinery rotational
speed;
U2 rectifier input voltage;
Alpha Rectifier phase shifting control angle;
Id direct current return route electric current;
The r0 inversion 换相 lead angle namely each interphase
current initial station is opposite to this nature 换相 angle;
U inversion trades flows 重叠?
Phi Air gap magnetic flux.
Rotational speed n and the air gap magnetic flux phi will have
the inverse ratio, if air gap magnetic flux phi oversized, will be
able to suppress the rotational speed the rise, will enable the
rotational speed not to be able to achieve the rated value, will cause
the incorporation overtime starting defeat. After the analysis,
the test 整步 incorporation stage exciting current greatly has two
main reasons:
如前所, when enters 整步 the incorporation stage, the
excitation control mode transfers by the permanent magnetic flux take
the electrical network voltage as the goal adjustment electrical
machinery terminal voltage. Its target is causes the electric
motor terminal voltage U end and the electrical network voltage U net
error in 2%. When rotational speed n is bigger than 95% cuts
整步 the stage from the acceleration period, because rate of voltage
rise far quickly to rotational speed ascending velocity, when like
this causes n approximately is 95%, U end = (100%-2%) U net, also is
the air gap magnetic flux phi big, namely the exciting current is big,
moreover so long as the U end the exciting current no longer carries
on the adjustment in (100%±2%) the U net scope, when finally causes
n=100%, electrical machinery terminal voltage nearby on limiting
value.
Carries on the test to the lock-on relay to discover its voltage
peak-to-peak value match is obviously unreasonable, its peak-to-peak
value match is 1.05U the net = U end. Adds the preceding factor
the influence, causes the incorporation voltage peak-to-peak value
control goal actually is 1.07U the net = U end, causes the exciting
current oversized, other situations slightly have the change,
rotational speed n cannot achieve the rated value, causes the
incorporation defeat.
(3) countermeasure measure
According to this situation the lock-on relay voltage
peak-to-peak value match adjustment is 0.975U the net = U end, 整步
the stage exciting current obviously drops, is 70A to 85A between,
eliminated the incorporation defeat phenomenon.
4.2 encoders breakdowns
(1) breakdown phenomenon
On July 1, 2001, because other breakdowns cause three to
agglutinate 1#, at the same time the 2# host platoon the engine off,
after the main platoon meets the starting requirement, starts the 1#
host platoon, inverts the control unit MC2315 appearance in the
starting process "ERR2" the breakdown (zero electric current
overtime), causes the starting defeat. Then starts the 2# host
platoon, similar breakdown starting defeat.
(2) fault analysis
The zero electric current overtime usually is because
the rotor position examines the mistake or the MC2315 board breakdown
causes. Here uses the photoelectricity encoder survey rotor
position and the rotational speed, this kind of equipment thermostable
ability is bad, because the continual high temperature weather, the
environment hyperpyrexia, continues in 65° above. According to
点检 inspected the record, the encoder signal 7, 8 channels already
was not the standard square-wave, the performance remarkable
deterioration. Basic may conclude the breakdown is because the
encoder signal irregularity causes. Because the replacement
encoder time is longer, may consider first cools the encoder, the
observation use effect, then decided whether replaces the encoder.
Triggers the angle cancellation when the synchronous motor
noramal work, the encoder measured the fast function, closes the
encoder power source. Simultaneously improves in the workshop to
ventilate the condition, reduces the ambient temperature.
Lengthens the encoder life.
4.3 crystals thyratrons short-circuit the
breakdown
(1) breakdown phenomenon
In July, 2001 some fortification ended, starts the 1#
host platoon, discovered the electric motor is motionless, according
to tightly stops the button termination starting. After carries
on some inspections, starts the 2# host platoon, the breakdown
phenomenon is invariable. The concrete phenomenon is:
After the electric motor excitation investment, the electric
motor sound responded normal (has electric current to pass).
After the main return route invests, the electric motor sound
response is normal, but does not rotate. The firing set direct
current demonstrated and hypothesis 440A slightly has the deviation.
(2) fault analysis
Starts the 1# host platoon electric motor to be
motionless. Creates this kind of situation the possible reason
to include: Does not have the exciting current or the exciting
current insufficient, has not advocated the loop current or the host
loop current insufficient, the encoder position examination is not
correct, but also has the electric motor itself question to create the
starting torque to be insufficient.
Because in successively and recent surely repairs, the electric
motor machinery, the electrical parameter are completely normal,
moreover also is two Taiwan Telegraphic Transmission motive similar
breakdown, may temporarily not consider electric motor itself in here.
Urges the floppy disk electric current demonstration normally,
the electric motor diode breakdown has not reported to the police,
when exciting current investment electric motor sound normal, may
think the excitation return route is normal.
First replaces the encoder, after but replaces the encoder to
start the 1# host platoon breakdown phenomenon to be invariable,
explained has nothing to do with with the encoder. The electric
motor electric current sound response is normal, explained the
electric current truly has flowed the stator coil. We discovered
the three phase ac 进线electric current is not balanced.
Carries on the inspection to the rectifier, discovered 软起?in the installment rectification bridge the 1# crystal thyratron
short-circuits. The replacement crystal thyratron, the starter
movement is normal.
To falls presses the transformer, the crystal thyratron carries
on the inspection, discovered 软起?the installment rectification
bridge 1# crystal thyratron short-circuits, rectification bridge
schematic diagram like chart 2 shows.
Chart 2 crystal thyratron rectification
bridge schematic diagram
In this equipment, the rectifier uses the speed,
electric current Shuanghuan controls, does not have the direct
examination direct current return route the electric current, but is
exchanges the return route electric current through the examination to
calculate the direct current. The rectification bridge crystal
thyratron work order is in turn 12, 23, 34, 45, 56, 61, if the 1#
crystal thyratron penetrates, in 12 leads passes the period, the
direct current return route has the electric current to flow, thus has
the electric current in the electrical machinery stator coil to flow.
As a result of starting current restriction in 20%, but the
electrical machinery speed is zero, namely the counter electromotive
force is zero, therefore the rectifier crystal thyratron triggers the
angle quite to be big. When triggers the 3# crystal thyratron,
because ab by way of 1#, the 3# crystal thyratron short-circuits, the
direct current return route does not have the electric current to
pass. Falls presses the transformer short-circuit impedance to
be very big (8.6%), has limited the short-circuit current; At
the same time, because the alternating current increases, the system
idea figures out the direct current feedback to increase, the control
system through the adjustment, promptly adjusts the crystal thyratron
to trigger the angle, triggers when the next crystal thyratron,
triggered the angle to be very big, limits the alternating current to
continue to increase, therefore the corresponding crystal thyratron,
the quick melt has not had the chain-reaction damage. Because
actual flows in the electrical machinery electric current not to be
big, enables the electric motor to start.
(3) breakdown lesson
Because the direct current ammeter undulation not
promptly observes, on was objective has increased the breakdown
processing difficulty. As well as because subconscious believed,
the crystal thyratron short-circuits can have the correlation crystal
thyratron and correspond the quick melt the chain-reaction, causes the
breakdown magnification, therefore on is subjective has not taken the
possibility which the crystal thyratron penetrates, also increased the
breakdown process time in the certain degree. But in fact
because has used the Gao Lougan special-purpose transformer, occurs
when short-circuits the accident, has limited the short-circuit
current, simultaneously the electric current assigns only has the
rating 20%, has limited alpha the angle, also reduced the
short-circuit current harm.
(4) countermeasure measure
Each time the main platoon pre-operational, must survey
the crystal thyratron resistance number; In the start process
carries on the monitoring to the three-phase current.
5 concluding remark
The Baoshan Steel Corporation three agglutinates the
host exhaust air blower in to go into production the initial period,
the starting defeat breakdown are more, above is several quite typical
breakdowns. We have not relied on the outside, independently
solves the problem which in the system exists. Besides has taken
the measure which front states, but also surely is being repaired,
carries on the on-line adjustment experiment according to the plan
branch to all spare parts, the guarantee complete spare parts supply,
as well as familiar equipment performance. In three years,
already has not recently broken down starting defeat.
The frequency conversion starts the large-scale synchronous
motor, the starting steady, completely has not also attacked to the
electrical network, the reliability is high, domestic and foreign has
applied quite widely. This kind of equipment maintenance,
breakdown processing also becomes an important research topic, if the
method, the measure are appropriate may effectively reduce the
maintenance of equipment cost, reduces the fault time.
|
