Sizing The DOL Motor Starter Parts (Contactor, Fuse, Circuit Breaker and Thermal Overload Relay)

Calculate size of each part of DOL motor starter for the system voltage 415V, 5HP three phase house hold application induction motor, code A, motor efficiency 80%, motor RPM 750, power factor 0.8 and overload relay of starter is put before motor. Basic Calculation of Motor Torque and Current Motor Rated Torque (Full Load Torque) = 5252xHPxRPM Motor Rated Torque (Full Load Torque) = 5252x5x750 = 35 lb-ft. Motor Rated Torque (Full Load Torque) = 9500xKWxRPM Motor Rated Torque (Full Load Torque) = 9500x(5×0.746)x750 = 47 Nm If Motor Capacity is less than 30 KW than Motor Starting Torque is 3xMotor Full Load Current or 2X Motor Full Load Current. Motor Starting Torque = 3xMotor Full Load Current. Motor Starting Torque = 3×47 = 142Nm. Motor Lock Rotor Current = 1000xHPx figure from below Chart/1.732×415 Locked Rotor Current Code Min. Max. A 1 3.14 B 3.15 3.54 C 3.55 3.99 D 4 4.49 E 4.5 4.99 F 5 2.59 G 2.6 6.29 H 6.3 7.09 I 7.1 7.99 K 8 8.99 L 9 9.99 M 10 11.19 N 11.2 12.49 P 12.5 13.99 R 14 15.99 S 16 17.99 T 18 19.99 U 20 22.39 V 22.4 As per above chart Minimum Locked Rotor Current = 1000x5x1/1.732×415 = 7 Amp Maximum Locked Rotor Current = 1000x5x3.14/1.732×415 = 22 Amp. Motor Full Load Current (Line) = KWx1000/1.732×415 Motor Full Load Current (Line) = (5×0.746)x1000/1.732×415 = 6 Amp. Motor Full Load Current (Phase) = Motor Full Load Current (Line)/1.732 Motor Full Load Current (Phase) = 6/1.732 =4Amp Motor Starting Current = 6 to 7xFull Load Current. Motor Starting Current (Line) = 7×6 = 45 Amp 1. Size of Fuse Fuse as per NEC 430-52 Type of Motor Time Delay Fuse Non-Time Delay Fuse Single Phase 300% 175% 3 Phase 300% 175% Synchronous 300% 175% Wound Rotor 150% 150% Direct Current 150% 150% Maximum Size of Time Delay Fuse = 300% x Full Load Line Current. Maximum Size of Time Delay Fuse = 300%x6 = 19 Amp. Maximum Size of Non Time Delay Fuse = 1.75% x Full Load Line Current. Maximum Size of Non Time Delay Fuse = 1.75%6 = 11 Amp. 2. Size of Circuit Breaker Circuit Breaker as per NEC 430-52 Type of Motor Instantaneous Trip Inverse Time Single Phase 800% 250% 3 Phase 800% 250% Synchronous 800% 250% Wound Rotor 800% 150% Direct Current 200% 150% Maximum Size of Instantaneous Trip Circuit Breaker = 800% x Full Load Line Current. Maximum Size of Instantaneous Trip Circuit Breaker = 800%x6 = 52 Amp. Maximum Size of Inverse Trip Circuit Breaker = 250% x Full Load Line Current. Maximum Size of Inverse Trip Circuit Breaker = 250%x6 = 16 Amp. 3. Thermal Overload Relay Thermal Overload Relay (Phase): Min. Thermal Overload Relay setting = 70%x Full Load Current(Phase) Min. Thermal Overload Relay setting = 70%x4 = 3 Amp Max. Thermal Overload Relay setting = 120%x Full Load Current(Phase) Max. Thermal Overload Relay setting = 120%x4 = 4 Amp Thermal Overload Relay (Phase): Thermal Overload Relay setting = 100% x Full Load Current (Line). Thermal Overload Relay setting = 100%x6 = 6 Amp 4. Size and Type of Contactor Application Contactor Making Cap Non-Inductive or Slightly Inductive ,Resistive Load AC1 1.5 Slip Ring Motor AC2 4 Squirrel Cage Motor AC3 10 Rapid Start / Stop AC4 12 Switching of Electrical Discharge Lamp AC5a 3 Switching of Electrical Incandescent Lamp AC5b 1.5 Switching of Transformer AC6a 12 Switching of Capacitor Bank AC6b 12 Slightly Inductive Load in Household or same type load AC7a 1.5 Motor Load in Household Application AC7b 8 Hermetic refrigerant Compressor Motor with Manual O/L Reset AC8a 6 Hermetic refrigerant Compressor Motor with Auto O/L Reset AC8b 6 Control of Restive & Solid State Load with opto coupler Isolation AC12 6 Control of Restive Load and Solid State with T/C Isolation AC13 10 Control of Small Electro Magnetic Load ( <72VA) AC14 6 Control of Small Electro Magnetic Load ( >72VA) AC15 10 As per above chart: Type of Contactor = AC7b Size of Main Contactor = 100%X Full Load Current (Line). Size of Main Contactor = 100%x6 = 6 Amp. Making/Breaking Capacity of Contactor = Value above Chart x Full Load Current (Line). Making/Breaking Capacity of Contactor = 8×6 = 52 Amp.

Smart and Safe Protective Shutdown with Selectivity

From the point of view of the operational safety and reliability of an entire low-voltage installation, it is usually desirable to specifically isolate the part of a system affected by a short-circuit in order to prevent spreading of the fault. Selectivity is intended to ensure that the protective shutdown is as close as possible to the location of the fault so that unaffected installation components can continue to operate normally. IEC 61439 standard – The new standard for low-voltage switchgear and controlgear ASSEMBLIES – Applies to enclosures for which the rated voltage is under 1000 V AC or 1500 V DC. This is often also desired for safety reasons and in IEC 60439-1 (low-voltage switchgear assemblies) addressed for installations that require a high level of continuity in current supply. In buildings and industrial plants, radial distribution networks are the norm. In radial distribution systems there are several protective devices in series, usually with decreasing rated currents from the supply end to the load end. While the operational currents decrease from the supply end to the load end, in the event of a short-circuit the same fault current will flow through all the protective devices connected in series. By a cascading of the trip characteristics it must be ensured that only the respective protective device that is closest to the location of the fault is activated and hence the fault is selectively limited to the smallest possible part of the installation. We saw in one of the previous technical article Simplify Downstream Installation with Cascading – that cascading actually makes protection system cheaper by simplifying the downstream installation (e.g. circuit breakers)

wake measurements behind An array of Two Model Wind Turbines (mechanical project)

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During the last decades the exploitation of energy from the wind has become one of the most promising renewable energy technologies. The main strive in today’s development of wind turbines is to increase the efficiency of the turbine and to build bigger rotors that are able to extract more power out of the wind.

When it comes to the planning and designing of a wind park, also the aerodynamic interactions between the single turbines must be taken into account. The flow in the wake of the first row turbines is characterized by a significant deficit in wind velocity and by increased levels of turbulence. Consequently, the downstream turbines in a wind farm cannot extract as much power from the wind anymore. Furthermore, the additional turbulence in the wake could be a reason for increased material fatigue through flow-induced vibrations at the downstream rotor.

The main focus of this experimental study is to investigate the local velocity deficit and the turbulence intensities in the wake behind an array of two model wind turbines. For two different turbine separation distances, the wake is scanned at three different downstream positions. The experiments are performed at the wind tunnel (1.9m x 2.7m cross section) at NTNU Trondheim using two model wind turbines with a rotor diameter of 0.9m. A hot wire probe is used to scan the wake behind the model turbines in defined positions.

Moving axially downstream the velocity deficit in the wake gradually recovers and the turbulence intensity levels slowly decrease. Furthermore, a gentle expansion of the wake can be observed. The wake profiles measured in close distances behind the rotor are characterized by evident asymmetries. Further downstream in the wake turbulent diffusion mechanisms cause a more uniform and more symmetrical flow field. Moreover, the turbulence intensity behind the second wind turbine is found to be significantly higher than behind one unobstructed turbine.

Also, considerably higher velocity deficits are found in the near wake behind the second turbine compared to the wake behind one unobstructed turbine. However, the velocity profile at five rotor diameters downstream in the wake behind the second turbine is already very similar to the velocity distribution behind the first turbine. Furthermore, the velocity field and turbulence intensity distribution in the wake behind the second turbine is more symmetrical and more uniform than behind the first turbine.

Chaos-based Random Number Generator in Finite Precision Environment (ECE/EEE Project)

Yet having a very long history, how to generating good random number sequences still remains as a technical challenge. Although some mechanical ways, such as tossing a coin or rolling a dice, are commonly accepted as good random sources, they are obviously not been able to fulfill the requirements of most of the real-world applications, in which high throughput and good quality are generally required.

For more than half century, different random number generators have been proposed. Recently, we have witnessed an active involvement of another branch of sciences in this topic, in particularly, aiming for cryptographical applications. Due to the distinct properties of chaos, including random-like dynamics, continuous broadband frequency spectrum, high sensitivity on initial conditions and system parameters, etc, the use of chaos in random number generation and cryptographical applications has aroused tremendous interests.

However, the actual realization environment is usually ignored in most of the chaos-based designs, for which an infinite precision is commonly assumed. As pointed out by some researchers, if a chaotic system is to be implemented in finite precision, its dynamics will be greatly deviated from its original one, and hence some nice properties will be vanished.

In this thesis, the use of chaotic maps or chaotic systems for the generation of random number under a finite precision environment is to be studied. Firstly, the adverse effects on the characteristics of the chaotic maps and chaos-based random number generators are investigated in details, when quantization errors occur through the evolution of the associated chaotic maps. In order to tackle with these effects, a novel high-dimensional chaos-based post-processing function is designed. With such data post-processing, the statistical quality of the generated random sequence can be greatly improved and can fulfill the up-to-date standards. From the experiments, it shows that the newly designed technique outperforms all the other existing post-processing methods, both in terms of performance and speed.

Finally, two practical designs of chaos-based random number generators are suggested for 32-bit and 8-bit precision environments. With a simple cascade structure of a chaotic map and the chaos-based post-processing function, a fast and simple chaos-based random number generator is designed in a 32-bit machine. An UDP secure chatting system is then developed, in which an effective encryption scheme is designed based on the 32-bit chaos-based random number generator. For the 8-bit environment, a chaotic circuit together with the proposed post-processing function is used. Good random number sequences can be generated and its quality is confirmed by statistical tests. This provides a unique solution for such a low precision system environment, which is still commonly found in industrial and consumer markets.

Neraj p mani

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