Hot Mill Volt/VAr Support
6.9 kV direct Connect
Single Stand Reversing
3minutes, 7 passes, 120 adjustments
Millions of relaible Operations
Via Remote Monitoring
5,000 HP Shredder Support
Dynamic support since 2006
Meets utility requirements
15% increased tons/hour

Two 7,000 HP motors on one 12.47kV bus.  Voltage sags during starts made starting dicey. 
Utility sag was greater than allowed.

SOLUTION:                                                                                                                                                                            
12 MVAR-rated Dynamic VAr System, sized to reduce 12.47 kV motor-start voltage sag from 11% (uncorrected) to 3.5%.  The sag on the utility transmission system was reduced from 7% to <2%.The modular TSC design resulted in a system designed to reliably meet the starting requirements, allowing the customer to avoid paying for un-needed capacity.  In service since 2006, this system has over 99.95% availability, having experienced a total of 4 components failing in a single incident.

The modular TSC design resulted in a system designed to reliably meet the starting requirements, allowing the customer to avoid paying for un-needed capacity.  In service since 2006, this system has over 99.95% availability, having experienced a total of 4 components failing in a single incident.

Customer preferred this solution over a soft-starting system (unable to satisfy utility sag requirements and still start motor) and over a VFD for starting (cost and simplicity).  Unit is deemed “must run.”  Refinery cannot operate significant process trains when it is not available.

When a newly-enhanced control system became available, customer elected to upgrade the unit in the field.  T-Star performs remote monitoring and assistance as requested.   All graphics shown on these pages were accessed directly  from the unit’s smart control system.

 

 

SPEED CONSIDERATIONS:

“Will this response shown satisfy the utility?”

For events like motor starts, the answer is absolutely yes.  As IEEE-1159 shows, events of < 1 cycle are considered to be transients (“glitches”).The timing shown below approaches the maximum response time of the unit.  Even under those circumstances, all phases respond within <1 cycle of the event occurring.   As a result, the impact of the motor start + unit on the power system is a transient (events like lighting strikes or switching operations), rather than a short term  variation (“droop”, “sag” or “flicker”), and is measured and treated accordingly.  Without the unit, the “short term event” would last 7-8 seconds. 

The impact of this transient on other equipment at the facility or on the power system is negligible.  The most common standard for equipment ride-through is the ITI/CEBMA curve. This widely-used standard  required equipment to “ride-through” a 40% sag of 1-cycle duration, and 100% sag for <1/2 cycle.  The utility gets a sag reduced to an un-noticed transient.  The unit-supported start ensures the client (and others on the circuit) have no problems with other equipment.  The client gets fast, reliable starts for their 7,000 HP synchronous motors.

 Measured Response Times:

Phase
Response Order

Time from Event
(sec)

Time from Event
(cycles)

B

0.0053

0.318

C

0.0113

0.678

A

0.0165

0.99

NOTE:  Actual event response time varies based on the phase angle at the time current flow triggers a response.  The responses shown at above and at right approach the theoretical maximum response time for this event.
Measureable motor current flow begins as the Phase A window closes, almost 120° (0.33 cycle) before Phase B responds. Any earlier and Phase A would have responded later and phases B and C would have responded in less elapsed time.