Asynchronous motor braking Schneider Electric - Training – Induction motors braking Method for stopping pp g the motors ● There are many ways to stop Speed Stop order Controlled stop Free wheeling Dynamic braking Time Schneider Electric - Training – Induction motors braking Dynamic braking or hypersynchronous braking Q4 Torque Q1 MOTOR PHASE ORDER : 1-2-3 Tn N’n >Ns Ns N’n n Nn N Q3 Schneider Electric - Training – Induction motors braking Speed Q2 MOTOR PHASES ORDER: 1-2-3 Hypersynchronous yp y braking g ● Braking without specific external device Rectifier D1 D2 D3 T1 Rd L1 L2 L3 D4 D5 Inverter Filter Vdc D6 T3 T5 Way of energy M 3~ C T2 T4 T6 Driving load Load DC Bus The energy is limited at 1/2 CV² => The capacitor will quickly reach maximum voltage The energy can also go in the discharge resistor and also in the drive control supply => Maximum braking at about 20% Tn Schneider Electric - Training – Induction motors braking Hypersynchronous yp y braking g ● Example of a cycle with light load Motor speed DC Bus voltage Motor torque Acceleration Schneider Electric - Training – Induction motors braking St d state Steady t t Braking (generator) Hypersynchronous yp y braking g ● The braking without accessories can be performed in 2 ways: ● BRA = YES : B Braking ki R Ramp A Auto-adaptation t d t ti : ●The ramp is automatically change in order not to go over the maximum DC bus voltage for BRA (a little below the overvoltage DC Bus trip level). ● BRA = DYN_A , Dyn B ou Dyn C (Specific to ATV61 or 71): ●Same thing than with BRA but with special algorithm that enhance losses inside the motor and cables Idem to increase the braking torque torque. ●This king of braking must remain ”exceptional” in the way that the energy is dissipated in heat inside the motor or cables and repetitive use can lead to overheat for both motor and cables. ●Example : A 400kw fan stops in free wheeling in 500s and with BRA enabled stops in 200s. With Dyn C braking, stop is achieved in 50s. (1 stop per day). Schneider Electric - Training – Induction motors braking Hypersynchronous yp y braking g ● Braking with BRA enabled: DC Voltage g Vdc Overvoltage (OBF) Vdc max Speed St order Stop d If BRA active, no trip but a longer stop time If BRA disabled, disabled trip of the drive and free wheeling Set ramp (DEC) Time Schneider Electric - Training – Induction motors braking Hypersynchronous yp y braking g ● DynA, B or C braking with ATV61 et 71 ● ex: motor/drive 7.5 kW, SVCU law ● inertia of 8 time motor inertia ● Ramp of 0.1s, deceleration from 60hz to 0Hz BRA=DYNA braking time =2.5s BRA=YES braking time 6.5s Speed Torque Schneider Electric - Training – Induction motors braking External braking g device: resistor ● Braking with a braking resistor Rectifier bridge D1 D3 D2 T1 T3 T5 Tf L1 L2 L3 PA D4 Rb: Braking resistor Inverter D6 D5 PB M 3~ C T2 Braking T4 T6 Load Rb Schneider Electric - Training – Induction motors braking External braking g device: resistor ● Example of a cycle with high inertia and braking resistor DC bus voltage Motor speed Motor torque Rb current Schneider Electric - Training – Induction motors braking External braking g device: REGEN ● Braking with network braking unit (NBU) Rectifier D1 D2 Inverter Filter D3 T1 L1 L2 L3 T3 T5 M 3~ C D4 D6 D5 T2 T4 T6 Load d T1’ T3’ T5’ Energy back to the network T2’ T2 T4’ T4 Schneider Electric - Training – Induction motors braking T6’ T6 B ki iinverter Braking t External braking g device: REGEN ● Example of a cycle with high inertia and network braking unit M t speed Motor d DC bus voltage Motor torque q Regenerated current (*3) Schneider Electric - Training – Induction motors braking Other topologies p g ● Active Front End (sine wave rectifier) Rectifier T1’ T3’ Inverter Filter T1 T5’ L1 L2 L3 T3 T5 M 3~ C T2’ T2 T4’ T4 T6’ T6 T2 T4 T6 Load Sine wave current consumed and regenarated on the network At PF=1 (reactive power compensation available) Schneider Electric - Training – Induction motors braking Active Front End ● Example of a cycle with high inertia and AFE Motor speed DC bus voltage reguled at 600V Network current (*10) consumed then regenerated Schneider Electric - Training – Induction motors braking Dynamic y braking: g Conclusion ● Without any accessory ● Benefits : No extra cost for the customer ● Limitations: limited to 20% of torque (Value can change according to the drive power but decreasing with the power) ● With a braking resistor ● Benefit : Little extra cost and possibility to brake at 100% of torque or more ● Limitations: Li it ti wasting ti energy, allll iis ttransformed f d iin h heat. t ● With a REGEN module ● Benefit : Efficiency, possibility to connect modules in parallel, less thermal losses ● Limitations: Beware during running on emergency generator or islanded network: Risk of important overvoltage or overspeed of the generators. ● No network = No braking (Beware of emergency stop regulations) ● With AFE ● Benefit : No more harmonics problems, the current is quite sinus with a possibility to compensate the network cos φ (avoid a capacitor bank) ● Limitations: Same as REGEN + beware of EMC due to high frequencies on the network side Schneider Electric - Training – Induction motors braking Example p of a return on invest ● For hoisting ● Power Braking time per cycle Number of cycles per hour Operating hours per day Working days per year Energy costs NBU cost VW3A7210 - 120kW VW3A7814 - 112kW RB cost AFE cost VW3A7250-260-265 – 120kW ● Energy savings per year W = 52500 kWh / yyear W = Pf = 100kW tb = 10s n = 30/ h h = 18h / d d = 350d / y K = 0,1 EUR / kWh Rk= 18800 eur Ck= 7550 eur Ak= 9970 eur 100kW ⋅ 10s ⋅ 30 / h ⋅ 18h / d ⋅ 350d / y 3600 ● Costs savings per year: E = 5250 eur / year E =W ⋅K E = 52500 kWh / yyear ⋅ 0,1 eur / kWh ● R.O.I : could be shorter thanks to environmental policy or price agreement REGEN A = 2.14 years AFE A = 0.5 year 6 months 26 months A= ( RK − CK ) PB ⋅ tB ⋅ n ⋅ BT ⋅ K ⋅ F A= (18800eur − 7550eur) ⋅ 3600s 100kW ⋅10s ⋅ 30 / h ⋅18h / d ⋅ 0,1eur Schneider Electric - Training – Induction motors braking Example p of a return on invest ● For a conveyor ● Power Braking time per cycle Number of cycles per hour Operating hours per day Working days per year Energy costs NBU cost VW3A7203 – 11 kW RB cost VW3A7710 - 25kW ● Energy savings per year Pf tb n h d K RK CK W= W = 3208 kWh / year ● Costs savings per year : 100kW ⋅ 5s ⋅ 30 / h ⋅18h / d ⋅ 350d / y 3600 E =W ⋅K E = 321 eur / year = 10kW = 5s = 30/ h = 22h / d = 350d / y = 0,1 EUR / kWh = 5435 eur = 2860 eur E = 3208 kWh / year ⋅ 0,1 eur / kWh ● R.O.I : could be shorter thanks to environmental p policy y or p price agreement g A = 8.02 years Schneider Electric - Training – Induction motors braking A= (RK − CK ) PB ⋅ tB ⋅ n ⋅ BT ⋅ K ⋅ F A= (5435eur − 2860eur) ⋅ 3600s 10kW ⋅ 5s ⋅ 30 / h ⋅ 22h / d ⋅ 0,1eur
