Shoring up Power: Controlling flicker and sag at Port of Sept-Îles
The Port of Sept-Îles is the largest ore handling port in Canada. Open year-round, the port is characterized by its deep waters and 10 km wide semi-circular bay.
The port is composed of 12 docks, six of which belong to it. Each year, nearly 23 million tons of merchandise is handled, composed mainly of iron ore. Alumina, aluminum, petroleum coke, limestone and other material also transit through the port, as well as more than 400,000 tons of petroleum products.
Alumina and coke are offloaded, stored and shipped via conveyors to the nearby Aluminerie Alouette smelter.
The seaport equipment used to handle this raw material has 21 motors, varying form 50 to 2,000 HP. Two of the 800-HP motors and the single 2,000-HP motor are required to offload the alumina and coke from the ships and stored in existing silos; this equipment is operated and maintained by Aluminerie Alouette.
|Motors at Port of Sept-Îles
• One 2,000-HP motor powers a giant, 4.16-KV suction pump. This pump removes the alumina and coke from the ships and deposits it on conveyors leading to the storage silos. This motor is started with an autotransformer starter at 65 percent of its nominal rated voltage.
• Three 800-HP motors activate the silo blowers. These motors are started across the line.
• Several 400 and 900-HP motors activate blowers used to transport the alumina and coke from the storage silo to the plant. These motors start three to four times daily.
When these large motors start, they draw an inrush current that significantly exceeds their full load current. This occurrence often causes the supply voltage to sag.
To reduce these voltage sags, Schneider Electric had initially looked at the feasibility of using soft starters to accelerate the large motors in conjunction with fixed and automatic capacitor banks. The soft starters would start the motors, the fixed capacitors would help support the voltage during the start, and the automatic capacitor bank would correct the Power Factor during the normal seaport operation. This solution was not considered feasible because:
- The voltage sags would exceed the required three-percent limit; and
- Trying to further limit the inrush current with a lower voltage and starting current would exceed the motors’ thermal limits.
The most feasible solution, proposed and implemented by Schneider Electric, was a medium-voltage hybrid VAR compensator (HVC) rated at 3,950 MVAR. This solution injects real-time capacitive reactive power during the motor start-up to support the voltage.The medium-voltage HVC is a mix of active harmonic filter technology (AccuSine) with a fixed or automatic de-tuned capacitor bank (MV6000) that can inject reactive power into a network with a one-cycle response time. The AccuSine can inject lagging or leading VARs within 16.6 ms. The MV6000 supplies a fixed amount of VARs to the system and the AccuSine either cancels these VARs when there is no load, or adds to these VARs when there is an increased amount of VARs required by the load.
The primary sizing calculation done by Schneider for this project was based on the motor lock rotor amps. The company collected real-time measurements on site during the motor start-ups, including current, voltage, real power (kW), reactive power (kVAR) and apparent power (kVA). With this data, Schneider constructed a computer model with which they could simulate the effect of real time VAR injection in the electrical network at 4.16 KV.
“We liked this solution for several reasons,” says Richard Lapierre of Alouette. “First and foremost, this cost-effective solution meets Hydro-Québec’s voltage sag limit of three percent at the PCC, and corrects the power factor during our seaport operations. Second, it is compact enough to fit in the electrical room, thereby avoiding contact with airborne contaminants (coke and alumina). Third, we appreciated being able to run the motors while the HVC was being installed, thereby minimizing production stoppage.”
This is an edited article provided by Schneider Electric Canada.