46
EEE / Re: মনের কথা জানাবে যন্ত্র
« on: November 02, 2014, 12:19:49 PM »
Very helpful.
News:
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47
Faculty Sections / আগুন নেভানোর উড়ন্ত যন্ত্র
« on: November 02, 2014, 10:53:00 AM »
অনলাইন ডেস্ক: আগুন নেভাতে প্রয়োজনীয় যন্ত্রপাতি না থাকলে অগ্নিনির্বাপক দলকে অনেক সময় কঠিন সমস্যার মুখোমুখি হতে হয়। কখনো উচ্চতার জন্যও আগুন নেভানো কষ্টকর হয়ে পড়ে।তাই এসব ক্ষেত্রে আগুন নেভানোর কাজে সাহায্য করতে পারবে এমন একটি উড়ন্ত যন্ত্র তৈরির কাজে এগিয়ে এসেছে যুক্তরাষ্ট্রের ন্যাশনাল অ্যারোনটিকস অ্যান্ড স্পেস অ্যাডমিনিস্ট্রেশন (নাসা)।
নাসার গবেষকেরা ড্রোন বা চালকবিহীন ছোট বিমানসদৃশ যন্ত্র তৈরি করছেন, যা কোথাও আগুন লেগেছে কি না তা যেমন শনাক্ত করতে পারবে, তেমনি সেই আগুনের শিখা নিভিয়ে আগুন নিয়ন্ত্রণে আনতেও সাহায্য করবে।
এই অগ্নিনির্বাপ ড্রোনের নকশা করেছেন যুক্তরাষ্ট্রের ভার্জিনিয়াতে নাসার ল্যাংলি গবেষণা কেন্দ্রের গবেষকেরা।
নাসার অ্যারোস্পেস প্রকৌশলী মাইক লোগান জানিয়েছেন, এই অগ্নিনির্বাপক যন্ত্রে যে ক্যামেরা রয়েছে তার সাহায্যে আগুনের উৎপত্তিস্থল শনাক্ত করা যাবে।
ইতিমধ্যে ভার্জিনিয়ার পানগোতে মিলিটারি এভিয়েশন মিউজিয়ামে চালকবিহীন এই উড়ুক্কু যন্ত্রটির পরীক্ষাও চালানো হয়েছে।
ড্রোনটি ৪০ থেকে ৫০ মাইল বেগে ২০ থেকে ২৫ মিনিট পর্যন্ত উড়তে পারে।
নাসার গবেষকেরা ড্রোন বা চালকবিহীন ছোট বিমানসদৃশ যন্ত্র তৈরি করছেন, যা কোথাও আগুন লেগেছে কি না তা যেমন শনাক্ত করতে পারবে, তেমনি সেই আগুনের শিখা নিভিয়ে আগুন নিয়ন্ত্রণে আনতেও সাহায্য করবে।
এই অগ্নিনির্বাপ ড্রোনের নকশা করেছেন যুক্তরাষ্ট্রের ভার্জিনিয়াতে নাসার ল্যাংলি গবেষণা কেন্দ্রের গবেষকেরা।
নাসার অ্যারোস্পেস প্রকৌশলী মাইক লোগান জানিয়েছেন, এই অগ্নিনির্বাপক যন্ত্রে যে ক্যামেরা রয়েছে তার সাহায্যে আগুনের উৎপত্তিস্থল শনাক্ত করা যাবে।
ইতিমধ্যে ভার্জিনিয়ার পানগোতে মিলিটারি এভিয়েশন মিউজিয়ামে চালকবিহীন এই উড়ুক্কু যন্ত্রটির পরীক্ষাও চালানো হয়েছে।
ড্রোনটি ৪০ থেকে ৫০ মাইল বেগে ২০ থেকে ২৫ মিনিট পর্যন্ত উড়তে পারে।
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Faculty Sections / পানির নিচের রেসিং কার
« on: November 02, 2014, 10:51:45 AM »
অনলাইন ডেস্ক: জেমস বন্ডের ছায়াছবি থেকে অনুপ্রাণিত হয়ে পানির নিচের রেসিংকার বাজারে এনেছে হ্যামাশার স্ক্লেমার প্রতিষ্ঠান। স্থলভাগে তো বটেই, পানির নিচের মাটি ছুঁয়েও এটি রীতিমতো ঘণ্টায় ১২১ কিলোমিটার বেগে ছুটে যেতে পারবে। পানির সান্দ্রতা বাধা অতিক্রম করে কী করে এমন গতিবেগ অর্জন করবে গাড়িটি তা ভেবে নিশ্চয়ই অবাক হচ্ছেন। আমরা ভুলে থাকি যে বাতাস আমাদের চারপাশ থেকে প্রবল চাপের মধ্যে রেখেছে। এই চাপ তুচ্ছ করে যদি স্থলভাগে রেসিং কার সবেগে ছুটতে পারে, তো মানুষের বুদ্ধিমত্তার কাছে জলের নিচ কেন আর বাধা হয়ে থাকবে?
এ গাড়ি কোন বর্জ্য সৃষ্টি করে না। কারণ এটি জৈবজ্বালানী চালিত নয়, বরং বিদ্যুৎ চালিত। এঞ্জিন হিসেবে রয়েছে ৫৪ কিলোওয়াট ১৬০ নিউটনমিটারের তড়িচ্চালিত মোটর। বেগ দান করতে চাকা ছাড়াও এতে রয়েছে দুটো প্রপেলার যেগুলো ঘূর্ণন সৃষ্টি করে গাড়ির সমভরের পানি পেছনে ঠেলে দিতে পারে। এটাকে নৌকোর মতো করেও চালানো যায়। যে বন্ড ছায়াছবির কথা বলা হলো, তার নাম দ্য স্পাই হু লাভস মি। ছবিটিতে জেমস বন্ডের ভূমিকায় অভিনয় করেছিলেন জনপ্রিয়তম বন্ড রজার মুর। ছবিটি ১৯৭৭ সালে মুক্তি পেয়েছিল।
মাত্র বিশ লাখ মার্কিন ডলার ট্যাঁকে থাকলেই এ গাড়িটি নিজের করে নেয়া যাবে।
এ গাড়ি কোন বর্জ্য সৃষ্টি করে না। কারণ এটি জৈবজ্বালানী চালিত নয়, বরং বিদ্যুৎ চালিত। এঞ্জিন হিসেবে রয়েছে ৫৪ কিলোওয়াট ১৬০ নিউটনমিটারের তড়িচ্চালিত মোটর। বেগ দান করতে চাকা ছাড়াও এতে রয়েছে দুটো প্রপেলার যেগুলো ঘূর্ণন সৃষ্টি করে গাড়ির সমভরের পানি পেছনে ঠেলে দিতে পারে। এটাকে নৌকোর মতো করেও চালানো যায়। যে বন্ড ছায়াছবির কথা বলা হলো, তার নাম দ্য স্পাই হু লাভস মি। ছবিটিতে জেমস বন্ডের ভূমিকায় অভিনয় করেছিলেন জনপ্রিয়তম বন্ড রজার মুর। ছবিটি ১৯৭৭ সালে মুক্তি পেয়েছিল।
মাত্র বিশ লাখ মার্কিন ডলার ট্যাঁকে থাকলেই এ গাড়িটি নিজের করে নেয়া যাবে।
49
Faculty Sections / মহাবিশ্বে সত্যিই এলিয়েন রয়েছে!
« on: November 02, 2014, 10:50:32 AM »
অনলাইন ডেস্ক: মহাবিশ্বে অবশ্যই ‘এলিয়েন’ বা ভিনগ্রহী প্রাণীর উপস্থিতি রয়েছে এমনটাই দাবি করা হচ্ছে নতুন এক প্রামাণ্য চিত্রে । হাজারো কৌতূহল ও বিতর্ক উসকে দেওয়া এরিয়া ৫১’র সাবেক এক বিজ্ঞানী ডক্টর বয়েড বুশম্যান তাঁর জীবনে যে এলিয়েন ও তাদের ব্যবহৃত যান ‘উড়ন্ত সসার’ নিয়ে গবেষণা চালিয়েছেন, তাদের ব্যাপারে মুখ খুলেছেন। এমন একটি এলিয়েনের বর্ণনাও দিলেন তিনি।
বুশম্যানের মতে, এলিয়েনটির বয়স প্রায় ২৩০ বছর, উচ্চতা পাঁচ ফুট, হাতে ও পায়ে পাঁচটি করে ১০টি আঙুল ও তারা টেলিপ্যাথি অর্থাৎ, ইন্দ্রিয়ের কোনো সাহায্য ছাড়াই কারো মন পড়তে ও বুঝতে পারে। কারো চিন্তা ও অনুভূতি অনুধাবনের ক্ষমতাও রয়েছে এলিয়েনদের।
এলিয়েনদের ব্যবহৃত উড়ন্ত সসার বা অশনাক্তকৃত উড়ন্ত বস্তু (ইউএফও) নিয়েও দীর্ঘ গবেষণা চালিয়েছেন বলে জানান ওই বিজ্ঞানী। এ খবর দিয়েছে বার্তা সংস্থা এএনআই। দিনে ২৪ ঘণ্টা মার্কিন বিজ্ঞানীরা ইউএফওর গবেষণায় ব্যয় করেছেন বলেও প্রকাশ করেন বুশম্যান। গবেষকরা এলিয়েনদের প্রজাতিকে দুটি দলে ভাগ করেন।
একটি দলের নাম দেন ‘র্যাংলার’ বা কলহকারী ও অপরটির ‘রাসলার’ বা গবাদিপশু চোর।
বুশম্যানের মতে, এলিয়েনটির বয়স প্রায় ২৩০ বছর, উচ্চতা পাঁচ ফুট, হাতে ও পায়ে পাঁচটি করে ১০টি আঙুল ও তারা টেলিপ্যাথি অর্থাৎ, ইন্দ্রিয়ের কোনো সাহায্য ছাড়াই কারো মন পড়তে ও বুঝতে পারে। কারো চিন্তা ও অনুভূতি অনুধাবনের ক্ষমতাও রয়েছে এলিয়েনদের।
এলিয়েনদের ব্যবহৃত উড়ন্ত সসার বা অশনাক্তকৃত উড়ন্ত বস্তু (ইউএফও) নিয়েও দীর্ঘ গবেষণা চালিয়েছেন বলে জানান ওই বিজ্ঞানী। এ খবর দিয়েছে বার্তা সংস্থা এএনআই। দিনে ২৪ ঘণ্টা মার্কিন বিজ্ঞানীরা ইউএফওর গবেষণায় ব্যয় করেছেন বলেও প্রকাশ করেন বুশম্যান। গবেষকরা এলিয়েনদের প্রজাতিকে দুটি দলে ভাগ করেন।
একটি দলের নাম দেন ‘র্যাংলার’ বা কলহকারী ও অপরটির ‘রাসলার’ বা গবাদিপশু চোর।
50
Faculty Sections / Re: জাপানে বিষাক্ত গ্যাসে কঠিন হয়ে পড়েছে উদ্ধারকাজ
« on: November 01, 2014, 09:45:15 AM »
Very critical task.
52
Faculty Sections / Re: সোমবার চালু হচ্ছে অ্যাপল পে
« on: November 01, 2014, 09:43:37 AM »
Good to know that.
53
Faculty Sections / Re: মঙ্গলে রহস্যময় হাড়!
« on: November 01, 2014, 09:43:02 AM »
very interesting.
54
Faculty Sections / Re: মুখ ধোয়ার সময়ে যে ভুলগুলো আমরা প্রায়ই করে থাকি
« on: October 19, 2014, 05:24:07 PM »
Should avoid it.
55
Faculty Sections / Re: রাষ্ট্রপ্রধান হওয়া এক আদিবাসী রাখালের গল্প
« on: October 19, 2014, 05:23:25 PM »
Very interesting
56
EEE / Re: Google to launch own mobile chat app: Economic Times
« on: October 19, 2014, 05:16:01 PM »
Informative.
57
EEE / Re: First space weather forecast centre opens in Britain
« on: October 19, 2014, 05:15:28 PM »
Interesting news.
58
EEE / Testing of power transformer – Measurement of impedance voltage and load loss
« on: October 19, 2014, 05:14:49 PM »
Purpose of the measurement
The measurement is carried out to determine the load-losses of the transformer and the impedanse voltage at rated frequency and rated current.
The measurements are made separetely for each winding pair (e.g., the pairs 1-2, 1-3 and 2-3 for a three-winding transformer), and furthermore on the principal and extreme tappings.
Apparatus and measuring circuit
On Figure 1 above (Circuit for the impedance and load-loss measurement) there are following figures:
G1 – Supply generator
T1 – Step-up transformer
T2 – Transformer to be tested
T3 – Current transformers
T4 – Voltage transformers
P1 – Wattmeters
P2 – Ammeters (r.m.s. value)
P3 – Voltmeters (r.m.s. value)
C1 – Capacitor bank
The supply and measuring facilities are not described here. Current is generally supplied to the h.v. winding and the l.v. winding is short-circuited.
Performance of the measurement
If the reactive power supplied by the generator G1 is not sufficient when measuring large transformers, a capacitor bank C1 is used to compensate part of the inductive reactive power taken by the transformer T2.The voltage of the supply generator is raised until the current has attained the required value (25…100 % of the rated current according to the standard 4.1).
In order to increase the accuracy of readings will be taken at several current values near the required level. If a winding in the pair to be measured is equipped with an off-circuit or on-load tap-changer. the measurements are carried out on the principal and extreme tappings.
The readings have to be taken as quickly as possible, because the windings tend to warm up due to the current and the loss values obtained in the measurement are accondingly too high.
It the transformer has more than two windings all winding pairs are measured separately.
Results
Corrections caused by the instrument transformers are made to the measured current, voltage and power values. The power value correction caused by the phase displacement is calculated as follows:
Equation 4.1 - Power value correction formula
Where:
Pc = corrected power
Pe = power read from the meters
δu = phase displacement of the voltage transformer in minutes
δi = phase displacement of the current transformer in minutes
ϕ = phase angle between current and voltage in the measurement (ϕ is positive at inductive load)
K = correction
The correction K obtained from equation 4.1 is shown as a set of curves in Figure 4.2.
The corrections caused by the instrument transformers are made separately for each phase, because different phases may have different power factors and the phase displacements of the instrument transformers are generally different.
If the measuring current Im deviates from the rated current IN, the power Pkm and the voltage Ukm at rated current are obtained by applying corrections to the values Pc and Uc relating to the measuring current.
The corrections are made as follows:
Equation 4.2 - Power Pkma
The correction caused by the phase displacement of instrument transformers (Figure 2):
Figure 4.2 - Phase displacement of istrument transformers
Figure 4.2 – Phase displacement of istrument transformers
Where:
K – correction in percent,
δu – δi – phase displacement in minutes
cosδ – power factor of the measurement.
The sign of K is the same as that of δu – δi.
Mean values are calculated of the values corrected to the rated current and the mean values are used in the following. According to the standards the measured value of the losses shall be corrected to a winding temperature of 75° C (80° C, if the oil circulation is forced and directed).
The transformer is at ambient temperature when the measurements are carried out. and the loss values are corrected to the reference temperature 75° C according to the standards as follows.
The d.c. losses POm at the measuring temperature ϑm are calculated using the resistance values R1m and R2m obtained in the resistance measurement (for windings 1 and 2 between line terminals):
The additional losses Pamat the measuring temperature are:
Here Pkm is the measured power, to which the corrections caused by the instrument transformer have been made, and which is corrected to the rated current according to equation (4.2).
The short-circuit impedance Zkm and resistance Rkm at the measureing temperature are:
Equation 4.6 - Short-circuit impedance
Equation 4.6
Equation 4.7 - Resistance Rkm
Equation 4.7
Ukm is the measured short-circuit voltage corrected according to Equation (4.3);
UN is the rated voltage and
SN is the rated power.
The short circuit reactance Xk does not depend on the losses and Xk is the same at the measuring temperature (ϑm) and the reference temperature (75 °C), hence:
Equation 4.8
Equation 4.8
When the losses are corrected to 75° C, it is assumed that d.c. losses vary directly with resistance and the additional losses inversely with resistance. The losses corrected to 75° C are obtained as follows:
Equation 4.9
Equation 4.9
Where:
ϑs = 235° C for Copper
ϑs = 225° C for Aluminium
Now the short circuit resistance Rkc and the short circuit impedance Zkc at the reference temperature can be determined:
Equation 4.10
Equation 4.10
Equation 4.11
Equation 4.11
Results
The report indicates for each winding pair the power SN and the following values corrected to 75° C and relating to the principal and extreme tappings.
D.C. losses POc (PDC)
Additional losses Pac (PA)
Load losses Pkc (PK)
Short circuit resistance Rkc (RK)
Short circuit reaactance Xkc (XK)
Short circuit impedance Zkc (ZK)
The measurement is carried out to determine the load-losses of the transformer and the impedanse voltage at rated frequency and rated current.
The measurements are made separetely for each winding pair (e.g., the pairs 1-2, 1-3 and 2-3 for a three-winding transformer), and furthermore on the principal and extreme tappings.
Apparatus and measuring circuit
On Figure 1 above (Circuit for the impedance and load-loss measurement) there are following figures:
G1 – Supply generator
T1 – Step-up transformer
T2 – Transformer to be tested
T3 – Current transformers
T4 – Voltage transformers
P1 – Wattmeters
P2 – Ammeters (r.m.s. value)
P3 – Voltmeters (r.m.s. value)
C1 – Capacitor bank
The supply and measuring facilities are not described here. Current is generally supplied to the h.v. winding and the l.v. winding is short-circuited.
Performance of the measurement
If the reactive power supplied by the generator G1 is not sufficient when measuring large transformers, a capacitor bank C1 is used to compensate part of the inductive reactive power taken by the transformer T2.The voltage of the supply generator is raised until the current has attained the required value (25…100 % of the rated current according to the standard 4.1).
In order to increase the accuracy of readings will be taken at several current values near the required level. If a winding in the pair to be measured is equipped with an off-circuit or on-load tap-changer. the measurements are carried out on the principal and extreme tappings.
The readings have to be taken as quickly as possible, because the windings tend to warm up due to the current and the loss values obtained in the measurement are accondingly too high.
It the transformer has more than two windings all winding pairs are measured separately.
Results
Corrections caused by the instrument transformers are made to the measured current, voltage and power values. The power value correction caused by the phase displacement is calculated as follows:
Equation 4.1 - Power value correction formula
Where:
Pc = corrected power
Pe = power read from the meters
δu = phase displacement of the voltage transformer in minutes
δi = phase displacement of the current transformer in minutes
ϕ = phase angle between current and voltage in the measurement (ϕ is positive at inductive load)
K = correction
The correction K obtained from equation 4.1 is shown as a set of curves in Figure 4.2.
The corrections caused by the instrument transformers are made separately for each phase, because different phases may have different power factors and the phase displacements of the instrument transformers are generally different.
If the measuring current Im deviates from the rated current IN, the power Pkm and the voltage Ukm at rated current are obtained by applying corrections to the values Pc and Uc relating to the measuring current.
The corrections are made as follows:
Equation 4.2 - Power Pkma
The correction caused by the phase displacement of instrument transformers (Figure 2):
Figure 4.2 - Phase displacement of istrument transformers
Figure 4.2 – Phase displacement of istrument transformers
Where:
K – correction in percent,
δu – δi – phase displacement in minutes
cosδ – power factor of the measurement.
The sign of K is the same as that of δu – δi.
Mean values are calculated of the values corrected to the rated current and the mean values are used in the following. According to the standards the measured value of the losses shall be corrected to a winding temperature of 75° C (80° C, if the oil circulation is forced and directed).
The transformer is at ambient temperature when the measurements are carried out. and the loss values are corrected to the reference temperature 75° C according to the standards as follows.
The d.c. losses POm at the measuring temperature ϑm are calculated using the resistance values R1m and R2m obtained in the resistance measurement (for windings 1 and 2 between line terminals):
The additional losses Pamat the measuring temperature are:
Here Pkm is the measured power, to which the corrections caused by the instrument transformer have been made, and which is corrected to the rated current according to equation (4.2).
The short-circuit impedance Zkm and resistance Rkm at the measureing temperature are:
Equation 4.6 - Short-circuit impedance
Equation 4.6
Equation 4.7 - Resistance Rkm
Equation 4.7
Ukm is the measured short-circuit voltage corrected according to Equation (4.3);
UN is the rated voltage and
SN is the rated power.
The short circuit reactance Xk does not depend on the losses and Xk is the same at the measuring temperature (ϑm) and the reference temperature (75 °C), hence:
Equation 4.8
Equation 4.8
When the losses are corrected to 75° C, it is assumed that d.c. losses vary directly with resistance and the additional losses inversely with resistance. The losses corrected to 75° C are obtained as follows:
Equation 4.9
Equation 4.9
Where:
ϑs = 235° C for Copper
ϑs = 225° C for Aluminium
Now the short circuit resistance Rkc and the short circuit impedance Zkc at the reference temperature can be determined:
Equation 4.10
Equation 4.10
Equation 4.11
Equation 4.11
Results
The report indicates for each winding pair the power SN and the following values corrected to 75° C and relating to the principal and extreme tappings.
D.C. losses POc (PDC)
Additional losses Pac (PA)
Load losses Pkc (PK)
Short circuit resistance Rkc (RK)
Short circuit reaactance Xkc (XK)
Short circuit impedance Zkc (ZK)
59
EEE / A transformer is only as strong as its weakest link
« on: October 19, 2014, 05:11:37 PM »
Transformer rating
Capacity (or rating) of a transformer is limited by the temperature that the insulation can tolerate. Ratings can be increased by reducing core and copper losses, by increasing the rate of heat dissipation (better cooling), or by improving transformer insulation so it will withstand higher temperatures.
A physically larger transformer can dissipate more heat, due to the increased area and increased volume of oil.
A transformer is only as strong as its weakest link, and the weakest link is the paper insulation, which begins to degrade around 100 °C. This means that a transformer must be operated with the “hottest spot” cooler than this degradation temperature, or service life is greatly reduced.
Presspahn - A proven surface insulation material, resistant to high voltage and a high capacity for impregnation with transformer oil (by UKi - one of Europe’s largest suppliers of electrical insulation materials)
Presspahn – A proven surface insulation material, resistant to high voltage and a high capacity for impregnation with transformer oil (by UKi – one of Europe’s largest suppliers of electrical insulation materials)
Reclamation typically orders transformers larger than required, which aids in heat removal and increases transformer life.
Ratings of transformers are obtained by simply multiplying the current times the voltage. Small transformers are rated in “VA,” volts times amperes.
As size increases, 1 kilovoltampere (kVA) means 1,000 voltamperes, 1 megavoltampere (MVA) means 1 million voltamperes. Large generator step-up (GSUs) may be rated in hundreds of MVAs.
A GSU transformer can cost well over a million dollars and take 18 months to 2 years or longer to obtain.
Each one is designed for a specific application. If one fails, this may mean a unit or whole plant could be down for as long 2 years, costing multiple millions of dollars in lost generation, in addition to the replacement cost of the transformer itself.
This is one reason that proper maintenance is critical.
Capacity (or rating) of a transformer is limited by the temperature that the insulation can tolerate. Ratings can be increased by reducing core and copper losses, by increasing the rate of heat dissipation (better cooling), or by improving transformer insulation so it will withstand higher temperatures.
A physically larger transformer can dissipate more heat, due to the increased area and increased volume of oil.
A transformer is only as strong as its weakest link, and the weakest link is the paper insulation, which begins to degrade around 100 °C. This means that a transformer must be operated with the “hottest spot” cooler than this degradation temperature, or service life is greatly reduced.
Presspahn - A proven surface insulation material, resistant to high voltage and a high capacity for impregnation with transformer oil (by UKi - one of Europe’s largest suppliers of electrical insulation materials)
Presspahn – A proven surface insulation material, resistant to high voltage and a high capacity for impregnation with transformer oil (by UKi – one of Europe’s largest suppliers of electrical insulation materials)
Reclamation typically orders transformers larger than required, which aids in heat removal and increases transformer life.
Ratings of transformers are obtained by simply multiplying the current times the voltage. Small transformers are rated in “VA,” volts times amperes.
As size increases, 1 kilovoltampere (kVA) means 1,000 voltamperes, 1 megavoltampere (MVA) means 1 million voltamperes. Large generator step-up (GSUs) may be rated in hundreds of MVAs.
A GSU transformer can cost well over a million dollars and take 18 months to 2 years or longer to obtain.
Each one is designed for a specific application. If one fails, this may mean a unit or whole plant could be down for as long 2 years, costing multiple millions of dollars in lost generation, in addition to the replacement cost of the transformer itself.
This is one reason that proper maintenance is critical.
60
EEE / Rating Definitions Applied to Medium Voltage Fuses
« on: October 19, 2014, 05:10:03 PM »
Expulsion fuses are defined as follows:
Expulsion fuse
A vented fuse in which the expulsion effect of the gases produced by internal arcing, either alone or aided by other mechanisms, results in current interruption.
EATON's medium voltage expulsion fuses
EATON’s medium voltage expulsion fuses provide full-range fault protection for both indoor and outdoor, medium voltage distribution systems
In addition, medium voltage fuses are further classified as power fuses or distribution fuses as follows:
Power fuse
Defined by ANSI C37.42-1996 as having dielectric withstand (BIL) strengths at power levels, applied primarily in stations and substations, with mechanical construction basically adapted to station and substation mountings.
Distribution fuse
Defined by ANSI C37.42-1996 as having dielectric withstand (BIL) strengths at distribution levels, applied primarily on distribution feeders and circuits, and with operating voltage limits corresponding to distribution voltages.
These are further subdivided into distribution current limiting fuses and distribution fuse cutouts, as described below.
Current-limiting fuses interrupt in less than _ cycle when subjected to currents in their current-limiting range. This is an advantage as it limits the peak fault current to a value less than the prospective fault current as described above for low voltage fuses. This provides current-limiting fuses with high interrupting ratings and allows them to protect downstream devices with lower short-circuit ratings in some cases.
However, the same technologies that combine to give medium voltage current-liming fuses their current-limiting characteristics can also produce thermal issues when the fuses are loaded at lower current levels. For this reason, the following definitions apply to current-limiting fuses.
Backup current-limiting fuse
A fuse capable of interrupting all currents from its maximum rated interrupting current down to its rated minimum interrupting current.
General purpose current-limiting fuse
A fuse capable of interrupting all currents from the rated interrupting current down to the current that causes melting of the fusible element in no less than 1h.
Full-range current-limiting fuse
A fuse capable of interrupting all currents from its rated interrupting current down to the minimum continuous current that causes melting of the fusible elements.
Due to the limitations of backup and general purpose current limiting fuses, current-limiting power fuses have melting characteristics defined as E or R, defined as follows:
E-Rating
The current-responsive element for ratings 100 A or below shall melt in 300 s at an RMS current within the range of 200% to 240% of the continuous-current rating of the fuse unit, refill unit, or use link. The current responsive element for ratings above 100 A shall melt in 600 s at an RMS current within the range of 220% to 264% of the continuous-current rating of the fuse unit, refill unit, or fuse link.
R-Rating
The fuse shall melt in the range of 15 s to 35 s at a value of current equal to 100 times the R number. Similarly, distribution current-limiting fuses are defined by given characteristic ratings, one of which is the C rating, defined as follows:
C-Rating
The current-responsive element shall melt at 100 s at an RMS current within the range of 170% to 240% of the continuous-current rating of the fuse unit. A typical time-current curve for an E-rated current-limiting power fuse is shown in Figure 1.
The fuse in Figure 1 is a 125E-rated fuse. Note that the curve starts at approximately 250 A for a minimum melting time of 1000 s.
Care must be taken with backup and general-purpose current-limiting fuses so that the load current does not to exceed the E- or R-rating of the fuse. Failure to do this can result in the development of a hot-spot and subsequent failure of the fuse and its mounting. For fuses enclosed in equipment, this can have disastrous consequences since failure of the fuse and/or its mounting can lead to an arcing fault in the equipment.
Note that the boundary of the characteristic, denoting the minimum-melting current, should be further derated to take into account pre-loading of the fuse (consult the fuse manufacturer for details). Note that, as with low voltage fuses, the current-limiting fuse characteristic does not extend below .01 seconds since the fuse would be in its currentlimiting range below this interrupting time.
Expulsion fuse
A vented fuse in which the expulsion effect of the gases produced by internal arcing, either alone or aided by other mechanisms, results in current interruption.
EATON's medium voltage expulsion fuses
EATON’s medium voltage expulsion fuses provide full-range fault protection for both indoor and outdoor, medium voltage distribution systems
In addition, medium voltage fuses are further classified as power fuses or distribution fuses as follows:
Power fuse
Defined by ANSI C37.42-1996 as having dielectric withstand (BIL) strengths at power levels, applied primarily in stations and substations, with mechanical construction basically adapted to station and substation mountings.
Distribution fuse
Defined by ANSI C37.42-1996 as having dielectric withstand (BIL) strengths at distribution levels, applied primarily on distribution feeders and circuits, and with operating voltage limits corresponding to distribution voltages.
These are further subdivided into distribution current limiting fuses and distribution fuse cutouts, as described below.
Current-limiting fuses interrupt in less than _ cycle when subjected to currents in their current-limiting range. This is an advantage as it limits the peak fault current to a value less than the prospective fault current as described above for low voltage fuses. This provides current-limiting fuses with high interrupting ratings and allows them to protect downstream devices with lower short-circuit ratings in some cases.
However, the same technologies that combine to give medium voltage current-liming fuses their current-limiting characteristics can also produce thermal issues when the fuses are loaded at lower current levels. For this reason, the following definitions apply to current-limiting fuses.
Backup current-limiting fuse
A fuse capable of interrupting all currents from its maximum rated interrupting current down to its rated minimum interrupting current.
General purpose current-limiting fuse
A fuse capable of interrupting all currents from the rated interrupting current down to the current that causes melting of the fusible element in no less than 1h.
Full-range current-limiting fuse
A fuse capable of interrupting all currents from its rated interrupting current down to the minimum continuous current that causes melting of the fusible elements.
Due to the limitations of backup and general purpose current limiting fuses, current-limiting power fuses have melting characteristics defined as E or R, defined as follows:
E-Rating
The current-responsive element for ratings 100 A or below shall melt in 300 s at an RMS current within the range of 200% to 240% of the continuous-current rating of the fuse unit, refill unit, or use link. The current responsive element for ratings above 100 A shall melt in 600 s at an RMS current within the range of 220% to 264% of the continuous-current rating of the fuse unit, refill unit, or fuse link.
R-Rating
The fuse shall melt in the range of 15 s to 35 s at a value of current equal to 100 times the R number. Similarly, distribution current-limiting fuses are defined by given characteristic ratings, one of which is the C rating, defined as follows:
C-Rating
The current-responsive element shall melt at 100 s at an RMS current within the range of 170% to 240% of the continuous-current rating of the fuse unit. A typical time-current curve for an E-rated current-limiting power fuse is shown in Figure 1.
The fuse in Figure 1 is a 125E-rated fuse. Note that the curve starts at approximately 250 A for a minimum melting time of 1000 s.
Care must be taken with backup and general-purpose current-limiting fuses so that the load current does not to exceed the E- or R-rating of the fuse. Failure to do this can result in the development of a hot-spot and subsequent failure of the fuse and its mounting. For fuses enclosed in equipment, this can have disastrous consequences since failure of the fuse and/or its mounting can lead to an arcing fault in the equipment.
Note that the boundary of the characteristic, denoting the minimum-melting current, should be further derated to take into account pre-loading of the fuse (consult the fuse manufacturer for details). Note that, as with low voltage fuses, the current-limiting fuse characteristic does not extend below .01 seconds since the fuse would be in its currentlimiting range below this interrupting time.