Basler Electric SMC-250 - Manual (Page 3)

excitation current range of 1 to 4 Adc is specified by
SMC-250 style xxxxAxxx, and excitation current
range of 4 to 8 Adc is specified by style xxxxBxx, or
an excitation current range of 8 to 15 Adc is specified
by style xxxxCxxx.
Control Inputs
SMC-250 control inputs are typically received from
remotely-located control switches and contact inputs
from external devices. The SMC-250 has prepro-
grammed control inputs that can be configured at the
discretion of the user. Refer to the appropriate
interconnection diagram for control input functions
and terminal assignments.
Control Outputs
SMC-250 control outputs consist of preprogrammed
output contacts and output contacts available for
configuration by the user. All control output
connections are made at the SMC-250 plate/chassis
terminal blocks. Refer to the appropriate inter-
connection diagram for control output function and
terminal assignments.
Communication Provisions
Optional accessory devices communicate with the
SMC-250 via the Ethernet port of the DECS-250 or
BE1-11m.
Additional communication capability is provided
through an SMC-250 RS-485 communication port
which uses the Modbus™ RTU protocol. RS485
connections are made at plate/chassis terminals
TB1-54 (A), 55 (B), and 56 (shield).
Digital Excitation Control System DECS-250
The DECS-250 supplies regulated excitation power
to the motor field. It also monitors parameters to
control and limit the motor from operating beyond its
capabilities.
Detailed information about DECS-250 operation can
be found in Basler publication 9440300990. The
following paragraphs serve as an overview of DECS-
250 functions.
Regulation
Digital signal processing and precise regulation
algorithms enable the DECS-250 to accurately
regulate the level of excitation. Motor parameters are
monitored through user-supplied VTs and CTs.
Sensing of field voltage and current is obtained
directly from the field. Depending upon the regulation
mode in use, the DECS-250 compares all or some of
these monitored parameters with the operating
setpoint and provides regulated excitation power to
the field. Two DECS-250 regulation modes are
possible: Manual or Auto.
Manual Mode
In Manual mode, the DECS-250 regulates the level of
excitation power supplied to the field independently of
all motor operating conditions. This makes Manual
mode useful as a backup method of excitation control
if a loss of motor voltage sensing or current sensing
occurs. In an SMC-250 system, Manual mode is
configured for field current regulation (FCR). FCR is
selected automatically at system startup or manualy,
by the operator, during normal operation. When
operating in FCR mode, the DECS-250 regulates
only the level of field current. The operator must
manually vary the FCR setpoint in order to achieve
the desired motor operating conditions.
Auto Mode
During the motor startup sequence, the DECS-250 is
switched from FCR to Auto mode when the BE1-11m
determines that the level of ac motor current has
reached the nominal level. In Auto mode, the DECS-
250 measures the real power into the motor and
adjusts the field excitation to obtain the desired level
of reactive power (and power factor).
Auto Tracking
The setpoint of the active regulation mode is
automatically tracked (followed) by the inactive
control modes. This feature enables the initiation of
“bumpless” transfers between Auto and Manual
mode and vice versa. For example, if a loss of
sensing occurs while operating in Auto mode, the
auto tracking function will minimize the disturbance
that the transfer from Auto mode to Manual mode
could cause.
Limiters
As implemented in the SMC-250, the following limiter
functions are enabled in the DECS-250: under-
excitation, overexcitation, reactive power (var),
underfrequency/volts per hertz, upper setpoint, and
lower setpoint.
Underexcitation Limiter (UEL)
The DECS-250 compares the real power (kW)
flowing into the motor with the reactive power (kvar)
being supplied. If the reactive power decreases
below the UEL setpoint, the DECS-250 will increase
field excitation to maintain synchronism and avoid
tripping the motor offline. During an underexcitation
condition, the DECS-250 closes the SMC-250
General Limiting output contacts at terminals TB1-64
and 65.
If underexcitation persists and is not corrected, the
DECS-250 closes the SMC-250 Alarm output
contacts at terminals TB1-90 and 91.
Overexcitation Limiter (OEL)
If the level and duration of current applied to the field
exceeds the OEL settings, the DECS-250 will retract
further increases in field current and lower the current
to a safe level for the machine. The OEL operates at
three levels to permit short-term var boosting that
could be beneficial for the application. During over-
excitation limiting, the DECS-250 closes the SMC-
250 General Limiting output contacts (TB1-64, 65). If
Publication
9494900994
Revision
A
Instructions
Date
10/14
Page
3 of 6