Cach do dien tro noi dat bang dong ho vang nang

Cach Do Noi Dat

1. Ngat hoan toan nguon dien cap vao cong trinh. Dung but thu dien hoac dong ho van nang o thang AC (V~) de xac nhan khong con dien ap truoc khi cham vao he thong tiep dat. Buoc nay bat buoc de dam bao an toan.
2. Do dien tro giua day dat (earth wire) va buong dat (earth busbar). Chi so nay phai nho hon 1 ohm, chung to day dan dat con nguyen ven, khong bi dut, long hoac oxy hoa. Neu lon hon 1 ohm, can kiem tra lai toan bo duong dan tu tui dien chinh den he thong tiep dat.
3. Do dien tro giua day trung tinh (neutral) va buong dat. Gia tri nay giup phat hien som cac loi ve day trung tinh bi mat hoac tiep xuc kem tai tu dien.

Dong ho van nang chi do duoc dien tro noi dat o muc co ban, phu hop cho kiem tra nhanh tai cong trinh dan dung. Sai so phu thuoc vao chat luong tiep xuc, do am cua dat va thang do duoc chon. Do tai nhieu diem va lay trung binh de giam sai so. De co so lieu chinh xac cho bao cao ky thuat, can dung thiet bi do dien tro noi dat chuyen dung (earth resistance tester) phuong phap 3 cuc.

Cach Do Dien Tro Noi Dat Bang Dong Ho Van Nang

Dien tro noi dat (earth resistance) la chi so quan trong nhat danh gia hieu qua he thong tiep dat. He thong tiep dat chuan cho phep dong dien su co thoat xuong dat nhanh, bao ve nguoi va thiet bi. Theo TCVN 4756:2012, dien tro noi dat he thong dien ha ap (duoi 1000V) khong qua 4 ohm, he thong chong set khong qua 10 ohm. Kiem tra dinh ky chi so nay la bat buoc voi ky thuat vien dien.

Chuan bi: 1) Dong ho van nang co thang Ω do phan giai 0.1 ohm, uu tien True RMS nhu ZOYI ZT-301 hoac ZT-S2. 2) Que do silicone CAT III. 3) Diem tiep dat tham chieu (buong dat hoac cay tiep dat chinh). 4) Gang tay cach dien 1000V.

Quy trinh do: Chon thang Ω thap nhat (200 ohm). Cam que den vao COM, que do vao VΩHz. Lam sach be mat tiep xuc bang giay nham. Dat mot que len diem tiep dat, que con lai vao dat am. Doc gia tri sau 3-5 giay khi da on dinh. Lap lai 3 lan tai cac vi tri khac nhau, lay trung binh. Neu dong ho hien thi “OL”, dien tro qua cao – chuyen thang do lon hon hoac kiem tra lai tiep xuc.

Danh Gia Ket Qua

Dien tro noi dat duoc danh gia: < 5 Ohm = TOT (dat tieu chuan). 5-10 Ohm = CHAP NHAN DUOC (cong trinh tam thoi). 10-20 Ohm = CAN SUA (kiem tra moi noi, an mon). > 20 Ohm = NGUY HIEM (xu ly ngay).

Yeu to anh huong: Do am dat (dat am thap hon dat kho 20-50%). Loai dat (dat set tot nhat, dat pha cat kem 2-3 lan, dat da/soi cho dien tro rat cao). Kich thuoc cay tiep dat (dai 2.5-3m, ∅16mm la toi uu). Tuoi he thong (cang cu cang kem do an mon). Nen do 2 lan/nam, mot lan mua kho, mot lan mua mua, ghi chep ket qua de theo doi suy giam.

An Toan Khi Do Dien Tro Noi Dat

Truoc khi do dien tro noi dat, ngat toan bo nguon dien (ca nguon chinh va du phong nhu may phat, UPS). Kiem tra bang dong ho van nang thang AC de xac nhan khong con dien ap. Trang bi: gang tay cach dien 1000V, giay each dien, kinh bao ve. Que do silicone phai con nguyen vo bao, kiem tra day dan ky truoc khi dung. Tuyet doi khong dung que do tu che hoac khong ro nguon goc.

Khi lam viec ngoai troi, chon vi tri kho rao, co mai che. Do am cao gay sai lech ket qua. Neu dat qua uot, hoan cong viec. Voi he thong tram bien ap, can chu y dien ap buoc va dien ap tiep xuc – giu khoang cach it nhat 5m tu thiet bi hu hong. Khong cham tay vao phan kim loai que do trong qua trinh do.

Cay Tiep Dat Va Vi Tri Do

Cay tiep dat (earth rod) la thanh thep hoac dong đuc xuong dat. Tieu chuan: ∅16mm, dai 2.5-3m, đau co ren M8-M10 bat buong chep. Cay dong hoac thep boc dong cho dien tro thap hon nhung dat hon. Đo sau đong tu 0.8-2m tuy loai dat.

Vi tri do: 1) Truc tiep tren cay tiep dat – cho dien tro cua cay, can thao buong chep va lam sach đau cay. 2) Tren buong dat – dien tro tong toan he thong. 3) Tai điem cuoi – kiem tra suy giam tren duong dan. Luu y: neu do o vi tri 2 hoac 3 cho gia tri cao, can kiem tra tung noi. Hieu chuan dong ho bang cach noi tat que do: neu chi ve 0, que do tot; neu khac 0, can hieu chinh lai.

Meo Do Chinh Xac

1) Lam sach be mat tiep xuc bang giay nham min (400-600 grit). 2) Thay pin dong ho 3-6 thang/lan – pin yeu gay sai so 10-15% thang Ω. 3) Do o nhieu thang, chon thang cho gia tri nam 1/3-2/3 thang do. 4) Ghi log vao bang tinh de theo doi xu huong. 5) Dung que do nhoi ma vang de tiep xuc on dinh. 6) Dat dong ho tren mat kho khi lam viec ngoai troi. 7) Cho dong ho on dinh 3-5 giay truoc khi doc. 8) Khong cham tay vao kim loai que do trong khi do.

Thiet Bi Do Dien Tro Noi Dat Chuyen Nghiep

De do chinh xac sai so duoi 1%, can earth resistance tester nhu Kyoritsu 4105A, Fluke 1625-2 dung phuong phap 3 cuc (fall-of-potential): dong dong xoay chieu 10-50mA xuong dat, do dien ap roi giua 2 dien cuc phu cach 20-62m. Ket qua chinh xac den 0.01 ohm. Phuong phap 3 cuc can dat 2 cay tiep dat phu tren duong thang, can khong gian thong thoang.

Voi kiem tra nhanh gia dinh hoac nha xuong nho, dong ho van nang ZOYI ZT-301 hoac ZT-S2 la du dung, tiet kiem chi phi. Voi benh vien, tram vien thong, trung tam du lieu, bat buoc dung thiet bi chuyen dung de co giay chung nhan dat chuan. Clamp meter ZT-QB3 cung co the do dong dien ro qua day tiep dat ma khong can ngat he thong, rat tien cho bao tri.

Meo Su Dung ZOYI Hieu Qua

De khai thac toi da dong ho van nang ZOYI khi do dien tro noi dat: Chon thang Ω thap nhat (200 ohm tren ZT-301, ZT-S2). Dung auto-range neu co de tranh chon sai thang. Kich hoat Hold de “dong bang” gia tri khi do o vi tri kho. Kiem tra day dan bang mat thuong truoc moi lan dung – day dut ngam ben trong la loi thuong gap nhat.

ZOYI clamp meter ZT-QB3, ZT-QB9 co the do dong dien ro qua day tiep dat khong can ngat dien. Chi can kep vong quanh day dat, doc dong dien ro hien tai. Neu tren 30mA, he thong co van de can kiem tra ngay. Rat huu ich cho bao tri dinh ky nha may, toa nha.

Cac San Pham ZOYI Khuyen Dung

1) ZT-301 (8000 dem, 200-300K VND): True RMS, CAT III 600V, NCV, dien dung, tan so, nhiet do – lua chon so 1 cho do dien tro noi dat co ban. 2) ZT-S1 (4000 dem, IP67, 300-400K VND): chong nuoc cho nha may, cong truong. 3) ZT-S2 (6000 dem, IP67, 400-500K VND): nang cap cua ZT-S1, True RMS. 4) ZT-X (10000 dem, 1M VND): oscilloscope 100MHz. 5) ZT-225 (6000 dem, Bluetooth, 2-3M VND): desktop DMM, ghi log. 6) ZT-QB3 (600A kep, 400K VND): clamp meter, do dong ro. 7) ZT-QB9 (600A kep, 32mm lo, 500K VND): clamp meter lo to. 8) ZC-900 (3000A kep, 1.5M VND): cho tram bien ap. Goi 0904 579 990 de tu van.

Cau Hoi Thuong Gap (FAQ)

Bai Viet Lien Quan

• True RMS la gi?
• Cach do dien ap DC/AC
• Cach do dong dien
• Nguyen tac an toan