Rob Dannemiller Regional Sales Manager
Post Glover Largest Global Manufacturer of Power Resistors In business since 1892 All Fabrication Done on-site Total Control Exercised Over Processes Headquartered in Erlanger, KY 75,000 sq-ft facility Workforce of 100 people 20 Engineers on staff Excellent Reputation for Quality & Service Certified ISO-9001-2000 Products certified by CSA and UL www.postglover.com
What we do Dynamic Braking Motor Control Neutral Grounding Load Banks Filter Resistors Transit
Dynamic Braking Drive basics Resistor physics Limitations Fan cooling
Dynamic Braking
Drive System
Inside a VFD
Regeneration - Occurs when the motor turns faster than the synchronous speed of the applied frequency. Motor will act as a generator. Mechanical energy is converted to electrical energy. AC Power from the motor is rectified by the IGBT freewheeling diode. Normal input bridge can t handle the regeneration. Motor
Why Use Dynamic Braking
Regeneration Techniques - Electrical Dynamic Braking Chopper control circuitry monitors the DC bus voltage If regeneration causes the bus voltage to rise above a certain level, the chopper turns on and shunts the energy through a DB resistor 460 VAC Dynamic Brake or Chopper 650 Volts DC
Regeneration Techniques - Electrical Dynamic Braking Advantages Simple, low cost Controlled braking Stopping OR Decelerating to a new speed Removes energy from drive and dissipates heat in power resistor specifically designed for the task Suitable for decelerating and overhauling loads Disadvantages Energy is lost to heat Overheating can be a concern Environment Correct sizing and cooling Duty cycle and HP limited by economics and space
Braking Braking vs. Overhauling Application of force (by removing kinetic energy) to decelerate a load more quickly than it normally would by coasting to a stop (using friction, windage). Overhauling Mechanical brake Dissipate energy in brakes as heat Electrical brake (DC Injection Brake, Flux Brake) Dissipate energy in motor as heat Dynamic braking Draw energy from DC bus and dissipate as heat in external power resistor. Line Regeneration Draw energy from DC bus and return it to the line supply Motor being driven by external forces Dynamic braking Line Regeneration
How Dynamic Braking Works + DC Bus Braking resistor Voltage divider Chopper Module - DC Bus
Key Info Drive input voltage Minimum resistance, or Maximum braking current Drive horsepower Duty cycle Braking profile Braking torque
Choosing resistance Minimum resistance Determined by maximum current rating of chopper transistor and chopper turn-on voltage (R min = V DC Bus /I max ) Maximum resistance Dependent on maximum DC voltage and maximum power
Horsepower 1 minute 1ft
How many watts in 1 HP? 1joule 1watt Given that: sec 1joule 0. 7375 ftlb so 1ftlb 1. 355932 joules and 1HP 33,000 ftlb so 1HP 550 ftlb 1joule /sec 1watt therefore / min /sec 1HP [550 ftlb /sec][1.355932 joules / ftlb] 1HP 745.76 joules /sec 1HP 745. 76watts
Available Power Motor Wattage = Drive Horsepower x 746 Peak Wattage = MW x Braking Torque Braking torque is typically between 100 and 150% Braking resistance = DC bus2 /PW
Type of Load Constant Torque Conveyors Heat generated is same at all speeds Cooling system deteriorates at reduced speed unless equipped with blower or TENV Variable Torque Centrifugal Fans & Pumps Torque related to square of speed / Horsepower related to cube of speed Operation at low speed not a problem due to low torque requirement Motor enclosure not an issue Constant Horsepower Machine Tool Torque rises as speed decreases If motor run below base speed, size with low speed torque and maximum operating speed Motor enclosure critical due to high torque at low speed Run motor above base speed
Decelerating Load Current decays Mindful of stop time Power to the resistor is averaged
Power/Speed Regeneration Techniques Dynamic Braking Energy Dissipated During Fixed Torque Stop 1 pu Pwr (peak) Torque Power & Speed Area = (Pwr(pk) x T)/2 = E t=0 T Time
Decelerating load Resistor wattage = (PW x Duty cycle)/2 Duty cycle = Time on /Time total Resistors begin to saturate temperaturewise about 100 seconds
Overhauling Load Current constant Duty cycle greater than 50% Stop time in excess of 60 seconds
Overhauling load Resistor wattage = (PW x Duty cycle) Duty cycle = Time on /Time total Temperature consideration critical Peak current vs Average current
Power/Speed Regeneration Techniques Dynamic Braking Energy Dissipated During Overhauling 1 pu Pwr (peak) Torque Power & Speed Area = (Pwr(pk) x T)/2 = E Area = Pwr(pk) x T = E t=0 T Time
Environmental Considerations Atmosphere Dirty Air XP areas Temperature Ambient Wash down Excessive Vibration Access
Forced-air cooled dynamic braking Technical overview: Existing PGR design: System information: PGR part number: DBRA36FC-14879-1 Power: 450 kw cont.(total) Watt density: 25 W/in^2 Circuit resistance: 3.70 Ω (+/-) 5% at 25C Max temp rise: 350 C Unit dimensions: 31 x 31 x 114.1 inches Unit weight: 2100 lbs Fan information: Fan diameter: 24 inches Motor power: 5 hp (AC) Fan speed: 1750 RPM Estimated CFM: 6,000 CFM
Regeneration Techniques Electrical Dynamic Braking Design Considerations Energy dissipation over time (watt-seconds). A function of: Inertia Magnitude of speed change Duty cycle Decelerating vs overhauling Resistor wattage and ventilation Amount of braking torque A function of the peak power P = V 2 /R The lower the ohms, the higher the braking torque Limited by the current rating of the chopper
Rob Dannemiller Regional Sales Manager Robert.Dannemiller@postglover.com 859.803.1621 Dave Perrine Copley Controls Corporation 330.666.8174