Module 6. DRIVE APPLICATION ON CRANESspeedcontrol.co.za/downloads/AC10Installation.pdf · Module 6. Drive Application on Hot Charge Cranes. Xstrata Training – Module 6 Application

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Module 6. Drive Application on Hot Charge Cranes.

Xstrata Training – Module 6 Application to Hot Charge Cranes

6.1 Introduction. Page 1 This section provides what is hopefully useful, but not too detailed, information on the overall control setup for the 15t Hot Charge Cranes at CMI Plant, and on the 30 and new 35t Hot Charge Cranes at Lion Plant. They have in common the same drive control technology, with the slip-ring motor plus AC10 thyristor control on hoist drives, and cage motors plus GT 3000 frequency control on travel drives. The cranes are fully automatic, and the basic application is the same. They lift containers loaded with hot pellets to the top of a charge shaft. The container is transferred, lowered and contents discharged into one of six furnace bins. The emptied container is hoisted and returned to the charge shaft. It is lowered to the shaft bottom, and the cycle is complete. A new cycle starts on receipt of free-to-start and bin-selects commands to each crane PLC control system. The cranes operate 24/7, and clearly, overall reliability and functional precision are paramount. They are one crucial part of a highly-automated production process. Why AC10 on hoists and GT 3000 frequency controls on travels? The actual precision is in stopping over the six bins, and over the shaft, and this is what frequency control excels in. If a target is missed, time is wasted in re-locating to it. The CMI cranes started with ECB control on the travels (1975). They were upgraded to Statovar (primary thyristor) control, when it became available, and this was a big improvement. The 3rd and final upgrade was to GT 3000 frequency control, with new cage motors. The same combination is employed in the Hot Charge Cranes in Lion Phase 1, and in the new Phase 2 Project. In a similar way, the original ECB hoist systems were upgraded to AC10 control with the original slip-ring motors. This proved satisfactory, and we are proud the same combination is on the Lion Phase 1 and 2 cranes. Out of interest, a Chinese group is building in Vietnam what will be the worlds largest steel plant. The Chinese specified: no frequency control on hot metal hoists, only thyristor control. They say yes to frequency control on hot metal travel drives. There seems to be a commonality of thought on this one. This Module is concerned with application of AC10 and GT 3000 controls to the crane drives, and with the basic control technology employed. The systems differ somewhat due to time spans, and for the purpose of illustration in particular, it is convenient to base the document on the latest Phase 2 system. Page 2---




6.2 Hoist System. Page 2 The hot charge hoist has conventional heavy duty limit switches to monitor operation along the shaft:

An automatic Start is with the container at position 8 – stop in shaft. The charge and swivel chutes must be out. The out is proved with the sum of two HD sensing devices: 1- CH E50 metal roller lever limit switch. 2- Siemens MGF 150RAKX magnetic limit device with ZMM35MM magnet. The automatic cycle proceeds upon receipt of free-to-start and bin-select inputs to the PLC. Page 3---

Charge chute

Spillage chute

Out limits

Out limits

Bottom shaft limit

Drop weight

Container full weight

Trip wire

1 2 3 4 5 6 7 8 9

9-cam limits: 1- hoisted backup 2- hoisted 3- hoist slow-down 4- slow-down above bin 5- stop in bin 6- over lower in bin 7- slow-down in shaft 8- stop in shaft 9- over-lower in shaft

SCT 9-SL 9 cam service limit limit switch

SHAFT DEVICES

Container




6.2 Hoist System---. Page 3 The hoist lifts at slow speed between limits 8 & 7. It accelerates to rated speed to limit 3, and continues at slow speed to limit 2 – hoisted. The transition from shaft to crane is in this range. A second N/O contact in limit confirms the container is up, and the travel drives are enabled. For normal automatic or manual operation, the travel drives will function only if the container is up. Limit 1 is a back-up to limit 2 – slightly higher, and then an SCT 4002 FL final limit switch, with SS rope and drop-weight, will trip the whole crane system if the container lifts even higher. The three hoist brake systems would immediately apply. This situation should never occur.

The SCT 9-SL nine cam service limit switch is driven directly by the rope drum. Both are manufactured by SCT. They are real heavy duty devices. The SCT 9-SL cam shaft is geared down to turn 3000 over the shaft height, and the individual cams are set and locked. At shaft bottom is a CH E50 spring rod limit switch. This is an ultimate bottom trip switch. Also at shaft bottom is a trip wire around the shaft wall, operating a CH E50KL355 belt trip switch. The same arrangement is around the hand rails of the crab platform, also to implement an emergency stop, if pulled. They are commonly referred to as tarzan wires. A second SCT 4002 FL drop weight limit switch is connected to stop the hoist if the container still has material after a discharge cycle, into a furnace bin. It would mean the container failed to discharge. Only in Manual Mode can a loaded container be lowered back down the shaft. This same overall arrangement is on all charge shafts at both CMI and Lion Plants. Page 4---




6.3 Hoist AC10 System. Page 4 The strategic nature of the HC Cranes is such that each hoist drive system has duplex AC10 controllers. They operate on a semi hot standby basis, with changeover power and control terminals between the two controllers. The power links are connected to the colour terminals for drive 1, or the black terminals for drive 2. The two sets of control terminals connect drive 1 or drive 2. Since the pic, they are correctly labeled. Also, all power terminals are protected with sculptured plastic. The changeover arrangement is straightforward and practical. The two AC10 drives are fully tested during the commission phase, and experience has shown that a drive swap-over is infrequent, if at all. The duplex arrangement is a strong security feature. At Lion Plant, the two AC10 assemblies are Size 600 with SKT 760/18E disc power devices. On 525V, the assemblies are rated for 545 kW. The motor rating is 287 kW at S4 60% ED. The AC10 rating is very conservative. The ---/18E means the devices have a PIV (peak inverse voltage) rating of 1800V. This is the minimum withstand voltage when they are blocking. They are top quality Semikron (Germany) devices. The A2 control assembly is the suffix D (digital) version, and this and the A (analogue) version are set out in Module 3 in the manual. Smaller AC10-D systems are employed to control each crane motion on the Hot Metal cranes at both CMI Plant and Lion Plant. The power devices in them are SKKT Semipak units, also described earlier on. The cranes are operated from a cabin, with individual 4-notch (4-speed) master controllers. Page 5---




6.3 Hoist AC10 System---. Page 5 Within the data package, the schematic for the 35t hoist is 0250-SD-H. Every item throughout the control package is itemized (with makers part number) in the Components List. We will look at the principal items: Symbol. Detail. -Q1 NS400 H 400A main circuit breaker. This is a current

limiting breaker, with fault capacity 35 kA on 525V. -OL Newelec 330M Crane Protection Monitor, for S4 60% ED

duty. The device is fed from three 500/1A current transformers – CT1-3.

-MC LC1 F500 stator contactor with rating 355 kW AC-3 on 525V. -A1 & -A2 AC10-D size 600 power-control assemblies – page 4. -RC1 & -RC2 LC1 V320 FE7 vacuum rotor contactors. The contacts

operate in vacuum tubes. In theory, there is no contact wear.

-BCB1 & - BCB2 GV2 M10 690V 4-6.3A circuit breakers for service and emergency brakes.

-BC1 & -BC2 LC1 D12 12A contactors for service and emergency brakes. -ST2 & -ST3 LY 414N sealed control relays with LED. -H1 to -H10 XB4 BVG5 22 mm cluster LED indicating lamps, to provide

visual indication of trip faults to master relay MR. -MR LC1 D12 master relay. This must be set (=1) for the system

to operate.

Note the 35t hoist has CT-fed ammeters (0-500A) in each stator and rotor phase. The panel suite is in a control room, and it is very useful to see balanced stator and rotor currents. Each AC10 hoist also has a 90-0-90V DC meter, to indicate

physical motor ± speed, based on 60V = 1000 rpm. Page 6---




6.4 Hoist Rotor Resistor. Page 6 For the 35t Hoist: Frame RSK 400 M-6 Mechanical with Pe = 287 kW and Pm = 269 kW at S4 60% ED duty. Per makers table: RV = 460 RA = 393

Check: P-kW = RV × RA = 460 × 393 = 287 kW 630 630

Adjust RA to Pm level: RA-Pm = 393 × Pm = 287 × 269 = 368 A Pe 287

Motor k-Pm = RV = 460 = 0.72 Ω

√3 × RA √3 × 368

Design: R3 R2 R1 Σ

p-u Ω (k multiple) 0.05 0.18 0.27 0.5 p-u A (A multiple) 1.0 0.9 0.9 Actual:

Ω 0.06 0.12 0.26 0.35 A 368 331 331

Bank MG 30 × 2 MG 4 × 2 MG 4 × 2

Bank Ω 0.05 0.06 0.06 Bank A 360 310 310 Bank Qty 1 2 3 6

Total Ω 0.05 0.12 0.19

Ω used 0.05 0.12 0.19 0.36

Ω over 0.001 0.00 0.00 This is the composition of one phase, comprising six MG resistor banks. The three phases then are identical with the assembly:

Page 7---




6.5 Hoist Over-speed System. Page 7 The hot charge hoists (at Lion) as well as the main hoists on the 130t Hot Charge Cranes, have a sophisticated mechanical brake arrangement. The high speed shafts are equipped with both service and safety thrustor brakes. In addition, disc caliper brakes operate direct on to flanges on the rope drums. With correct control, emergency disc brakes provide maximum security, in the event of an over-speed or emergency trip situation. They ensure the rope drum, and not just the motor, is stopped. Over-speed means the rope drum is turning at a speed faster than the related rated motor speed, driving through the drive train. The hoists are AC10-controlled, and via independent tacho feedback, it monitors all motor speeds. The A128 Speed Loop Supervisor has a fixed trip at 120% speed. The system is stopped, with brakes applied. The drive must be reset, to allow a re-start. This is a strong security measure for any Class 4 AC hoist, with a slip-ring drive motor, and with thrustor brake(s) operating on the high speed drum. Hoists fitted with caliper disc brakes operating on the rope drum must have independent (out of the control) over-speed detection, with a critical set trip point. The Demag hoists have excellent EB brake systems. The rope drum speed is monitored by a direct-driven Baumer POG 10 + DSL Incremental Encoder with Integrated Speed Switch. Via a laptop, the device is precision set to trip at 110% speed. The contacts in it are self-monitoring for total security, and it has independent encoder output terminals. Page 8---




6.6 CT and LT Drives. Page 8 The Hot Charge Cranes are precision machines. The precision is in traveling at rated speed to a variety of targets – in this case six – then retarding to a precise slow speed close to the target, and then stopping exactly on the target. After discharge of load, the reverse procedure takes the crane back to the target of the hot charge shaft. The hoist then lowers to limit position 8 – stop in shaft – and the cycle is complete. Basic information on the plant will assist in describing the control functions in the automatic bin charging process. Furnace A is identical but mirror image of Furnace B. The six furnace A bins are left of the A hot charge shaft. If the shaft axis (to bins 1, 6 & 5) is taken as x, and the right angle axis (to bins 2. 3 & 4) is y, then simultaneous travel motion can take place in both x & y axes (cranes at Lion Plant). A travel cycle starts once the container is hoisted to limit position 2 – hoisted. Limit 2 has two contacts, one N/C to stop the hoist, and the other N/O to prove the container is correctly hoisted. Only then (with exception to special bypass functions) can the CT and LT drives go into operation. They are otherwise locked out. So for normal duty, the container must be UP, for the travel cycle to proceed. The LT motion alone starts if the bin-select input (to the PLC) is bin 1, 6 or 5. They are on the same axis as the shaft. Both CT and LT motions start with bin-select 2, 3 and 4. The drives go through the standard mechanical cycle set out in Mod 5 page 16, namely accelerate, run at full speed, decelerate , creep and stop, precisely on target. The container then lowers to limit 5 – stop in bin. The CT and LT drives are locked out. The cone lowers and container load discharges. The hoist lifts back to limit 2 (hoisted), and reverse CT and LT cycles then bring the container back to the shaft ordinates. Page 9---

Bin 1 Bin 6 Bin 5

Bin 3 Bin 4

Bin 2Hot chargeshaft

Hot chargeshaft

Plan viewB furnace

Plan viewA furnace




6.6 CT and LT Drives---. Page 9 For correct production, the accel’ (ta) and decel’ (tb) gradients are sharp, and the

creep time short, before stopping on target. The creep frequency is ± 4.0 Hz = 8% speed. On arrival on the designated stop target, the motors are halted (frozen) by application of DC injection braking, and the service brakes are applied. The need for precision control is obvious. For interest, a locked motor does not mean the machine it drives is stationary. There is a flexible coupling between the two – not unlike a spring. If the creep speed is high when the brake applies, the

remaining kinetic energy (J = 1/2mν2) sets up damped oscillations which take time to dissipate. This can be disruptive in terms of accuracy and time. Run speed is set between 50 & 60Hz. This is another good reason for frequency control – the run speed can be set above 50 Hz. Decel’ on the selected targets is initiated by a bi-stable limit switches positioned along the shop gantry for the LT motion, and along the crane gantry for the CT motion. The automation system is controlled from the S7 300 PLC in one panel of the control suite, positioned in the control room. Each has targets along the x and y axis for slowdown and stop. The setup for each stop position is based on a magnetic bi-stable limit switch for slowdown, and two binary proximity limit switches for the stop (and maintain) function. The arrangement is: There is one torque arm on the crab, and one on an end carriage. There is one bi-stable magnetic sensor along the crane and shop gantry, for each target position. Page 10---

Fine target Wide target

Prox switches Magnet

Turned 900

Bi-stable limit

Gantry

Limit arm on crane

Travel

SD & target sensors




6.7 Limit Sensors. Page 10 Above is a side view. The proximity target sensors are hard-wired on the crane, and the bi-stable magnetic sensors hard-wired in a straight line along the shop gantry for the LT motion, and along the crane gantry for the CT motion. The single mobile magnet (on limit arm) changes over the sensors as the arm passes over them. The stationary magnetic sensors are positioned to allow slowdown and creep on to the target stop. For the selected bin: Once the crane motion has stopped on the fine target, it is allowed to deviate by the width of the wide target. Sounds strange? The motions (x & y) must stay on target to lower and discharge, then to hoist and return to shaft. With the scale of the plant and thermal conditions, the building can heave and deviate one of the two motions off the fine target. This would be an error in the software program, and the automatic cycle would stop. The procedure then would be to complete the cycle in manual mode – wasting time. The allowed deviation is small (40 mm). It has no effect on the discharge process. Sensor reliability is vital. The Phase 1 cranes started with bi-stable (two stationary positions) mechanical fork limit switches. They were not ideal (mechanical wear), and were replaced with sealed bi-stable magnetic sensors and magnets. The result was good, and the same is implemented for the Phase 2 cranes. Sensor: MGF 150RAKX Magnet: ZMM 35MM The proximity sensors are E51 heavy duty units: Head: E51TD1 Body: E51SAL Page 11---

open closed

50-60 Hz

4 Hz

stop

deviate

Targets

y

x




6.8 GT 3000 Frequency Controllers. Page 11 On logic similar to that for the duplex AC10 hoist drives, duplex GT 3000 frequency controllers are also provided for the two travel drives. They also operate on a semi-hot standby basis, with changeover power and control terminals between each controller set. It’s all to do with ensuring a speedy return to production if a drive failure should occur. The two controllers in a drive set are obviously identical, each with a dedicated keypad, correctly programmed. One must never swop a keypad from a failed controller to another controller. A drive failure can impact onto a keypad, and even the keypad itself can fail. Despite a proven track record of reliability for the GT 3000 controller, the duplex arrangement is a wise precaution in this fully automatic production process. The travel motors are standard 400V cage units. The controllers are de-coupled from the supply by a 50 kVA 525/400V air-cooled double-wound transformer DY+N. This arrangement had its origin in CMI Hot Charge Cranes a long time ago, when they were converted to frequency control. It isolates the controllers from plant surges, and provides a clean earth connection. Arc furnaces are notorious for the generation of harmonics and transient surges. The GT 3000 controller particulars are:

Cross travel: 2 × SVGT 045 FDBFNNN Rating 52A 22 kW on 400V.

Long travel: 2 × SVGT 053 FDBFNNN Rating 65A 30 kW on 400V.

Keypad: 2 × SVGT AFK per crane motion. Each controllers is complete with internal line choke and brake chopper. The

top-mounted braking resistors are 15 Ω for cross travel, and 10 Ω for long travel drive. Page 12---




6.9 Controlling PLC and Desk. Page 12 The Hot Charge Cranes have both a manual and automatic control mode, determined by a 2-position selector switch on the control desk. With exception of emergency devices such as E-stop, pull wire and over-speed function, all logic as well as manual devices are directly connected as logic inputs to the Siemens S7 300 controlling PLC – 35t HC cranes. Logic devices are the sensors along the gantry, track and shaft. Manual devices are the desk-mounted controls – namely master controllers for Hoist, CT and LT motions – to set speed and direction, within ranges permitted by the control logic. By safety requirements, the desk E-stop button will directly trip crane power, and all brakes will apply. Desk controls and indication are set out to represent the position of bins and shaft, and movement of the crane motions between bins and shaft. Every sensor and position limit has a 22 mm cluster LED (zero wear) to show its status. Control desk Crane A. The three lamps representing each bin show the operator the bin selected, and indicate when the motions are close to target – the slowdown zone. The four blue lamps light ON TARGET. Page 13---

CT SD LT SD

BIN SELECT




6.10 Desks and Automation. Page 13 Control desk Crane B is content identical but with a mirror image layout for the furnace bins, relative to the charge shaft. Clearly, the desks are used only with the MAN – AUTO selector (above the E-stop button), in manual mode. Normal operation is in AUTO. It can be useful to just observe the progress of the cranes from the LED’s. The top-mounted pilot controls enable manual operation within the limits determined by plant sensors, and PLC logic. There are times when the cranes need to be driven beyond the normal limit footprint, as well as when the container is not fully hoisted. It can even be lowered on to the furnace top. Additional pilot controls enable out-of-norm maneuvers, but they are concealed inside the desks. The selectors are spring-return. One operator must hold the bypass selector inside the desk for the selected crane function, and another drive the crane from the desktop. Two operators must collude to implement out-of-norm maneuvers. Desk controls and indication are wired direct to an S7 300 PLC outstation, and this is connected by Profibus cable to the S7 300 PLC in the main control suite. Overall, each crane system is a modern example of control technology combined with drive technology. Page 14---




6.11 System PLC. Page 14 First to specify the desk-mounted master controllers: Hoist: VNS0 3 FU 18 AKER 20 CT – LT: VNS0 33 FU 18 AKVR 30.30 The Siemens S7 300 PLC operates on a Profibus network and the software program for the 35t cranes was designed by Consulting Engineers iControl in collaboration with Speed Control Tech’. The PLC (programmable logic controller) controls the crane in both automatic and manual mode. The function of the automatic program has reasonably been described in preceding sections. With the bin at shaft bottom (position 8), the hoist lifts on receipt of Bin-select and Free-to-Start inputs from the control room. Free to start meaning both swivel chutes are proven to be in the OUT position. The container is charged. It lifts to position 2 at the two speeds regulated by the system, and the described travel cycles then proceed. Following discharge and hoist, the reverse travel and hoist cycles bring the empty container back to Start position 8, where again it will be charged by the swivel chute, controlled by plant logic. The next cycle, to a new Bin-select, can then proceed. Manual operation from the desk controls gives an operator discretion over crane movements, providing operation is within the structured logic governing the automatic cycles. Then there are the various bypass functions controller from inside + outside the desk. The field and crane position sensors operate on 110V 50 Hz, and they input direct into the PLC. Both input and output modules operate on this crane control voltage. The full material configuration (CPU + I/O modules) of the PLC is detailed in Users Technical Document for the crane Page 15---




6.12 Crane Protection Panel (CPP). Page 15 The first panel in the suite is looked at last. The CPP receives 525V plant power and distributes power to the crane drives and supporting systems. Circuit breaker –Q1 (NS630 H) isolates the crane manually, and it trips electrically in event of an emergency function trip (E-stops and final limits, etc). This and the other breakers are current-limiting, with a fault clearing capacity of 34 kA on 525V. Main contactor – MC (LC1 F630) is closed by ON-OFF buttons in the desk, providing the system is healthy. As with each crane motion panel, a 22 mm yellow cluster LED (XB4 BVG5) indicates any trip, such as a control CB, within the panel. Circuit breaker –Q2 (NS80H MA) feeds out to the 50 kVA 525/400V isolation transformer feeding the CT & LT frequency controllers. Control transformer –T1 has a 55-0-55V secondary supplying 110V to the crane motions and field monitors. The secondary connects to an Isoloc 315 M earth leakage monitor. It monitors the resistance between earth and each 55V leg. The value is indicated on the device, and if it drops below a set value, triggers a small audible alarm plus indication on the desk (with alarm cancel button). A full earth control fault is limited to 1 mA, presenting no danger to personnel, and the plant continues to operate. This is a subject on its own, and proprietary information on the 315 M monitor is provided in the data pack manual for each crane. Alongside it is a ZORC 550V high energy suppressor. It is connected directly across the three incoming phases. It absorbs heavy supply side line transients – ever present in a steel production process. This is a really important item in the crane system with power electronics. Each corner of both crab and crane has a CMP 616 rail blower, and each blower has a GV2 ME06 circuit breaker to isolate and protect it. A blower trip does not stop the crane. It is simply indicated on the desk. Interface relays in this and other panels are LY 414 N (with large LED) and with MY 4 base. Page 16---




6.13 Other Items of Interest. Page 16 Junction Boxes. Sounds dull, but the quality and construction of JB’s does have an impact on crane reliability. Even JB’s break down. If internal insulation failures occur, the supply voltage can penetrate to delicate control cables, resulting in difficult (to find) stoppages – and damage to electronics. For this and any other contract, we take JB’s (very) seriously. Typical JB’s:

Installation at Demag works (130/50/20t Ladle Crane – AC10 systems):

Appreciation is extended to Demag Cranes and Components (Pty) Ltd for kind permission to publish the photos. Regards to all. BC (Chris) Conroy




Testing a 35t Furnace Charging Crane at Demag.

Module 6. DRIVE APPLICATION ON CRANESspeedcontrol.co.za/downloads/AC10Installation.pdf · Module 6. Drive Application on Hot Charge Cranes. Xstrata Training – Module 6 Application

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